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WCDMA Air Interface LZT 123 7279 R4A © Ericsson AB 2004 - 1 - WCDMA Air Interface STUDENT BOOK LZT 123 7279 R4A

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WCDMA Air Interface - 2 - © Ericsson AB 2004 LZT 123 7279 R4A DISCLAIMER This book is a training document and contains simplifications. Therefore it must not be considered as a specification of the system. The contents of this document are subject to revision without notice due to ongoing progress in methodology design and manufacturing. Ericsson assumes no legal responsibility for any error or damage resulting from the usage of this document. This document is not intended to replace the technical documentation that was shipped with your system. Always refer to that technical documentation during operation and maintenance. © Ericsson AB 2004 This document was produced by Ericsson AB. • It is used for training purposes only and may not be copied or reproduced in any manner without the express written consent of Ericsson. This Student Book LZT 123 7279 R4A supports course number EN/LZU 108 5306 .

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Table of Contents LZT 123 7279 R4A © Ericsson AB 2004 - 3 - Table of Contents 1 WCDMA WIRELESS TECHNOLOGY........................................... 7 IT’S ALL ABOUT SERVICES............................................................... 10 WCDMA BACKGROUND..................................................................... 10 WCDMA AIR INTERFACE.................................................................... 10 WCDMA MILESTONES.........................................................................11 EVOLUTION FROM 2G TO 3G.............................................................11 PRESENT FUNCTIONALITY ............................................................... 12 WCDMA RADIO ACCESS BEARERS RABS...............................................12 MULTIPLE ACCESS TECHNOLOGIES .........................................................14 TDMA TRANSMITTER ......................................................................... 15 WCDMA TRANSMITTER ..................................................................... 16 VOICE CODING..............................................................................................18 ADAPTIVE MULTI-RATE................................................................................21 ERROR DETECTION AND CORRECTION - CRC AND FEC CODING.........23 CHANNELIZATION CODES ...........................................................................37 SCRAMBLING CODES...................................................................................43 MODULATION ................................................................................................51 FILTERING .....................................................................................................53 2 WCDMA POWER CONTROL RAKE RECEIVER AND HANDOVER ................................................................................. 59 WCDMA RECEPTION ISSUES............................................................ 62 WCDMA RECEPTION ISSUES............................................................ 62 WCDMA POWER CONTROL............................................................... 63

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WCDMA Air Interface - 4 - © Ericsson AB 2004 LZT 123 7279 R4A MULTIPATH FADING............................................................................ 65 THE RAKE RECEIVER ........................................................................ 67 WCDMA HANDOVER........................................................................... 71 3 CAPACITY CONSIDERATIONS ................................................. 77 CELL PLANNING ................................................................................. 80 FDMA/TDMA...................................................................................................80 WCDMA ..........................................................................................................81 UPLINK CAPACITY.............................................................................. 84 CAPACITY MANAGEMENT................................................................. 88 ADMISSION CONTROL .................................................................................88 CONGESTION CONTROL .............................................................................89 4 WCDMA PHYSICAL LAYER....................................................... 91 3GPP..................................................................................................... 94 WCDMA OSI MODEL .....................................................................................99 WCDMA DOWNLINK ......................................................................... 102 LOGICAL CHANNELS ..................................................................................104 TRANSPORT CHANNELS ...........................................................................104 PHYSICAL CHANNELS................................................................................105 CHANNELIZATION CODE INDEX ...............................................................106 COMMON PILOT CHANNEL........................................................................107 PRIMARY COMMON CONTROL PHYSICAL CHANNEL AND SYNCHRONIZATION CHANNEL .................................................................107 SECONDARY COMMON CONTROL PHYSICAL CHANNEL ......................108 PAGING INDICATOR CHANNEL .................................................................109 DEDICATED PHYSICAL CONTROL AND DATA CHANNEL.......................110 MULTIPLEXING............................................................................................115 WCDMA UPLINK.................................................................................119 DEDICATED PHYSICAL CONTROL AND DATA CHANNEL.......................120 RANDOM ACCESS CHANNEL ....................................................................123

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Table of Contents LZT 123 7279 R4A © Ericsson AB 2004 - 5 - MULTIPLEXING............................................................................................123 HPSK MODULATION ...................................................................................125 5 WCDMA PROCEDURES........................................................... 129 BASE STATION DOWNLINK TIMING ............................................... 131 SYNCHRONIZATION PROCEDURE ................................................. 131 DOWNLINK SCRAMBLING CODES ............................................................131 SYNCHRONIZATION CODES......................................................................132 RANDOM ACCESS PROCEDURE.................................................... 136 DEDICATED CHANNEL PROCEDURE............................................. 141 WCDMA SOFT HANDOVER.............................................................. 142 6 ACRONYMS AND ABBREVIATIONS....................................... 145

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 7 - 1 WCDMA Wireless Technology Objectives Upon completion of this chapter the student will be able to: • Explain the fundamental principles of cellular WCDMA technology. • Explain and compare TDMA and WCDMA multiple access methods. • Explain on an overview level the WCDMA transmitter architecture. • Explain the data protection coding methods: CRC Coding FEC Coding Viterbi decoding block interleaving turbo codes. • Explain the use of channelization and scrambling codes. • Explain the modulation and filtering in a WCDMA system.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 9 - Contents IT’S ALL ABOUT SERVICES............................................................... 10 WCDMA BACKGROUND..................................................................... 10 WCDMA AIR INTERFACE.................................................................... 10 WCDMA MILESTONES.........................................................................11 EVOLUTION FROM 2G TO 3G.............................................................11 PRESENT FUNCTIONALITY ............................................................... 12 WCDMA RADIO ACCESS BEARERS RABS...............................................12 MULTIPLE ACCESS TECHNOLOGIES .........................................................14 TDMA TRANSMITTER ......................................................................... 15 WCDMA TRANSMITTER ..................................................................... 16 VOICE CODING..............................................................................................18 ADAPTIVE MULTI-RATE................................................................................21 ERROR DETECTION AND CORRECTION - CRC AND FEC CODING.........23 CHANNELIZATION CODES ...........................................................................37 SCRAMBLING CODES...................................................................................43 MODULATION ................................................................................................51 FILTERING .....................................................................................................53

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WCDMA Air Interface - 10 - EN/LZT 123 7279 R4A IT’S ALL ABOUT SERVICES Third Generation 3G networks can be implemented using a number of different technologies. As long as they can provide the wanted services that is all that is required. However some technologies have more advantages than others in terms of efficiency of spectrum usage and flexibility. WCDMA BACKGROUND In 1992 the World Administrative Conference WARC of the ITU International Telecommunications Union chose frequencies around 2 GHz as available for use by third generation mobile systems. Within the ITU these third generation systems are called International Mobile Telephony 2000 IMT-2000. Within IMT-2000 several different air interfaces are defined for third generation systems based on either Wideband Code Division Multiple Access WCDMA or TDMA technology. The same air interface WCDMA is to be used in Europe and Asia including Japan and Korea using the frequency bands around 2 Ghz. WCDMA AIR INTERFACE As well as WCDMA the other air interfaces that can be used are EDGE and cdma2000. EDGE Enhanced Data Rates for GSM Evolution can provide bit rates up to 500kbps within a GSM carrier spacing of 200kHz. Cdma2000 can be used as an upgrade for the existing IS-95 operators. Spectrum allocation in Europe Japan and Korea is 1920 – 1980 Mhz uplink and 2110 – 2170 Mhz downlink.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 11 - WCDMA MILESTONES In January 1998 the European standardization body ETSI decided upon WCDMA as the third generation air interface. Pre- commercial testing phase took place in Europe at the beginning of 2002. The first commercial network was opened in Japan during 2001 for commercial use in key areas EVOLUTION FROM 2G TO 3G As can be seen in Figure 1-1 below the second generation 2G networks are designed and optimized for circuit switched services such as voice and low bit-rate circuit switched data. They are not optimized for packet data and can offer at best a maximum data throughput of 14.4 kbps per timeslot. It should be noted that there are various enhancements becoming available such as GPRS and EDGE to improve the 2G network’s data handling capabilities to increase its data transfer rate and allow packet data services. Third Generation 3G networks on the other hand have been designed for data transmissions and support not only circuit switched voice and circuit switched data but also high-speed packet switched data as well as multi services.

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WCDMA Air Interface - 12 - EN/LZT 123 7279 R4A Circuit -Switched Voice Circuit -Switched Data Circuit -Switched AMR coded voice Circuit -Switched data Packet Data Streaming Short Message Service SMS 2G 3G Multiservice : AMR coded voice + Packet data Figure 1-1: From 2G to 3G. The demands on the 3G networks are going to be very different to the basic voice communication requirement of the 2G networks. This will require a very flexible air interface that can meet the demands of both circuit switched voice or data and packet services and handle these in the most efficient way. PRESENT FUNCTIONALITY The following Radio Functionality is included in the WCDMA Radio Access Network WCDMA RAN Phase 2.1. WCDMA RADIO ACCESS BEARERS RABS The purpose of a Radio Access Bearer RAB is to provide a connection segment using the WCDMA RAN for support of a UMTS bearer service. The WCDMA RAN can provide Radio Access Bearer connections with different characteristics in order to match requirements for different UMTS bearers. In Figure 1-2 the different RABs supported in the P2.1 WCDMA RAN are illustrated.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 13 - Conversational Speech 12.2 kbps Circuit switched Conversational CS Data 64 kbps Circuit switched Streaming 57.6 kbps Circuit switched Interactive Variable rate Packet Switched RACH/FACH 64/64 64/128 64/384 Combination of Conversational Speech and Interactive 64/64 Multi-RAB Figure 1-2: WCDMA Radio Access Bearers RABs The conversational speech RAB is tailored to 12.2 kbps Adaptive Multi Rate AMR speech and will also be used to carry emergency calls. Video telephony service may be offered across the Conversational 64 kbps Circuit Switched CS RAB. Streaming 57.6 kbps is used to support v.90 modem connections. The maximum data rate supported by the Interactive or Background Packet Switched PS RAB is 384 kbps in the downlink and 64 kbps in the uplink making it ideal for email or web browsing. The Multi-RAB is used for both 12.2 kbps AMR and PS 64/64 kbps.

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WCDMA Air Interface - 14 - EN/LZT 123 7279 R4A MULTIPLE ACCESS TECHNOLOGIES There are three basic air interface multiple access techniques frequency time and code division multiple access Figure 1-3. Frequency Division Multiple Access Each User has a unique frequency 1 voice channel per user All users transmit at the same time AMPS NMT TACS User 1 User 2 User 3 Frequency Each Transmitter has a unique Scrambling Code Each Data Channel has a unique Channelization code Many users share the same frequency and time IS-95 cdma2000 WCDMA Frequency Code Division Multiple Access Spread Spectrum Multiple Access Multiple Transmitters and Multiple Data Channels Each User has a unique time slot Each Data Channel has a unique position within the time slot Several users share the same frequency IS-136 GSM PDC Time Division Multiple Access User 1 User 2 User 3 User N Time Figure 1-3: Multiple Access Approaches. Frequency Division Multiple Access FDMA is very common in the first generation of mobile communication systems. Examples of systems using this technique are NMT TACS and AMPS. The available spectrum is divided into physical channels of equal bandwidth. One physical channel is allocated per subscriber. The physical channel allocated to the subscriber is used during the entire duration of the call and is unavailable for use by another subscriber during this time. In Time Division Multiple Access TDMA the available spectrum for one carrier is divided in time. The subscriber is allocated a set amount of time referred to as a time slot. Subscribers can only use the air interface for this amount of time. An example of a system that uses this principle is D-AMPS which explains why D-AMPS is sometimes called TDMA. Since other mobile telephony systems that use TDMA for example GSM also split the available frequency band into several distinct carriers in a sense they are hybrids using both TDMA and FDMA.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 15 - Wideband Code Division Multiple Access WCDMA allows many subscribers to use the same frequency at the same time. In order to distinguish between the users the information undergoes a process known as spreading that is the information is multiplied by a channelization and scrambling code hence WCDMA is referred to as a spread spectrum technology. This technology was first developed by the military to avoid the possibility of their signals being jammed or listened to by the enemy. TDMA TRANSMITTER The TDMA transmitter is illustrated in Figure 1-4. Data Multiplexer Data Multiplexer Transmit Gating Transmit Gating Control/ Signaling Data Filtering + RF Modulation Filtering + RF Modulation RF Out Sync. Bits User Data Channel N Error Protection Error Protection Timeslot Selector Error Protection Error Protection User Data Channel 1 Error Protection Error Protection Vocoder Vocoder Error Protection Error Protection The Multiplexer allows various data channels to share the same timeslot. The timeslot selector allows multiple transmitters to share the same carrier frequency by assigning a unique timeslot to each transmitter. Figure 1-4: TDMA Transmitter The voice channel is passed through a vocoder which produces a digital representation of the input analogue signal. After error protection this is fed into a data multiplexor where it is multiplexed with synchronization bits and control/signaling data and user data channels. This combined signal is passed to the transmit gating device. This allows transmission during the specified timeslot for a particular user in the way a ‘push-to-talk’ button is used in a two-way radio. This allows multiple transmitters to share the same frequency by assigning a unique time slot to each. Finally filtering and RF modulation is performed and the signal is passed to an antenna system.

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WCDMA Air Interface - 16 - EN/LZT 123 7279 R4A WCDMA TRANSMITTER The WCDMA transmitter Figure 1-5 looks similar to the TDMA transmitter with the synchronization control/signaling and multiple user data channels. However in this case neither time nor frequency is used to separate different users but codes in an operation known as spreading. In the case of the TDMA transmitter these data channels were time multiplexed. However the WCDMA transmitter simply multiplies each channel by a different binary code known as a channelization code. This process provides the necessary separation between the data channels which can then simply be added together in a summation device. The output of this block is a digital data stream that contains different logical levels depending on the number of channels that were added together. If for example two data streams that contain levels between +1 and -1 when added together will contain a stream that contains levels between +2 and –2. Three data streams added produce levels between +3 and -3 and so on. In reality this varying level depending on the number of channels cannot be sent to the modulator so each channel is weighted to ensure that the combined result is a fixed level. This explains why power is the shared resource. The WCDMA transmitter now needs some method of providing separation between this signal and other transmitters but cannot use time slots like the TDMA case. This separation is achieved by multiplying this composite signal by another binary code called a scrambling code. Filtering and RF modulation are then performed to produce an RF output that contains all the information from all the users at the same time and on the same frequency. It is important to note that this transmitter diagram is not accurate and is included merely to show some of the main points of the technology. The next transmitter diagram figure 1-6 is more realistic. The receiver needs to know the scrambling code to perform the reverse process and then use the same channelization codes to retrieve each data channel.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 17 - Filtering + RF Modulation Filtering + RF Modulation RF Out Linear Summation Linear Summation Control/ Signaling Data Sync. Bits User Data Channel N Error Protection Error Protection Error Protection Error Protection User Data Channel 1 Error Protection Error Protection Vocoder Vocoder Error Protection Error Protection Frequency User 1 User 2 User 3 ... Channelization code 4 Channelization code N Channelization code 3 Channelization code 2 Channelization code 1 Channelization Codes provide unique identification of each data channel Scrambling Codes SC provide unique identification of each transmitter Scrambling Code Scrambling Code Scrambling Code Scrambling Code Scrambling Code Figure 1-5: The WCDMA transmitter Figure 1-6 shows schematically the various blocks contained in a WCDMA transmitter detailed. Note that the 1:2 de-multiplexing part is only valid in the downlink. CRC Coding CRC Coding FEC Coding FEC Coding Maps digital bits to analog signals 0 → +1 1 → -1 Pre-coded data bits Pulse Shaping Filter Pulse Shaping Filter RF Out Data Channel 1 Data Channel N Σ Σ Channelization Code 1 Pulse Shaping Filter Pulse Shaping Filter I/Q Modulator I/Q Modulator Inter- leaving Inter- leaving CRC Coding CRC Coding FEC Coding FEC Coding Inter- leaving Inter- leaving D/A D/A I Q Allows for error detection in the receiver Allows for error correction in the receiver Improves error correction in the receiver Gives a unique identity to each data stream Contains transmitted frequency spectrum Allows both signals from I and Q branch to share the same RF bandwidth Data Symbols Chips I Q Modulation Symbols 1:2 Demux 1:2 Demux Provides 2x higher data rate WCDMA cdma2000 downlink 1:2 Demux 1:2 Demux I Q scrambling Code 1 Channelization Code n D/A D/A I Q I Q scrambling Code 1 Gives a unique identity to this transmitter I Q Figure 1-6: WCDMA Transmitter detailed Error detection and error protection of the data channels are performed using Cyclic Redundancy Check CRC coding Forward Error Correction FEC and interleaving. It should be remembered that this user data could be voice from a vocoder user data or control data.

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WCDMA Air Interface - 18 - EN/LZT 123 7279 R4A The next stage is to perform a 1:2 de-multiplexing of the stream downlink only. This effectively doubles the data rate by taking all the even bits from the input stream and placing them on the I- branch and all the odd bits onto the Q-branch. This step is used to take advantage of an RF modulation scheme known as I/Q- modulation. The data is then converted from a digital signal ranging from 0 to 1 to an analogue signal that ranges from –1 to +1. The error-protected signal is then multiplied by a particular channelization code to provide the necessary channel separation. This is necessary since all the channels will be added together which will produce a composite data stream. Scrambling of the signal is then performed using a complex multiplier effectively using a separate scrambling code for the I- and Q- branches. This complex scrambling code is generated using a linear shift register. The channels are then summed together. After pulse shape filtering the I- and Q-branch are passed to the I/Q-modulator which will produce an RF output that can be fed to the antenna system. Each of these stages is explained in more detail in the rest of this chapter. VOICE CODING A simple analogy to explain the concept of voice coding is to use that of a saxophone concert Figure 1-7.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 19 - Record the sax player onto a CD... ... and play back the CD 20 MB per song Write down the notes he plays... ... and have a friend play the same notes 20 kB per song Figure 1-7: Voice Coding Example: Two ways to hear the sax player. Suppose you have tickets for a concert but find that at the last minute you cannot attend. You then find someone else who can attend in your place. However this person offers you two choices: He/she can take a recorder and create a compact disk of the concert using perhaps 20MB of storage area per song or go to the concert and write down the notes as they are played creating perhaps only 20 KB per song. Obviously the first option produces the best reproduction of the concert since the second option involves someone playing the music from the recorded notes. However if this person is going to charge you for the amount of data required for each option the choice is not so simple. In the case of mobile communications where system bandwidth is at a premium the second option would be best suited since all users must share the same bandwidth. Less bandwidth per connection will allow more users in the system. In cordless phone systems Adaptive Differential Pulse Code Modulation ADPCM coding is used offering a 32kbps channel for each connection whereas the coding in GSM for example uses a vocoder that only requires a data channel at a rate of 13 kbps full- rate.

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WCDMA Air Interface - 20 - EN/LZT 123 7279 R4A Human speech is made up of two types of sounds: those produced by the vocal cords ‘ah’ ‘v’ and ‘mm’ which make up approximately 80 of the time and those produced by air passing through the teeth ‘ss’ ‘ff’ and ‘sh’. All that is required is to pass these sounds through the throat which will act as a filter and make the voice sound distinctive. The vocoder Figure 1-8 needs only to send noise and pitch parameters along with details of the resonance of the vocal tract filter H s. This will reduce the bandwidth required to transmit the voice. At the receiver the voice can be re-synthesized by combining the output of a white noise generator and a pulse generator to mimic the vocal cords. After passing the output through the filter to recreate the vocal tract a good representation of the original voice should be produced. Human Voice: ‘ss’ ‘ff’ ‘sh’ … 20 of time ‘ah’ ‘v’ ‘mm’ … 80 of time Transmitted Parameters 812 kb/s typical vs. 64 kbps for log-PCM 32 kbps for ADPCM Vocoder White Noise Generator Pulse Generator Σ Voice Re-Synthesis at the Receiver Noise parameters Pitch parameters Hs Filter poles correspond to resonances of the vocal tract Speech Output Hs Figure 1-8: Voice Coding

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 21 - ADAPTIVE MULTI-RATE The type of voice coding used for WCDMA Figure 1-9 is a combination of coding called Algebraic Code Excited Linear Predictive ACELP which uses codebook references to represent speech sounds and Adaptive Multi Rate AMR coding which allows different speech rates to be used depending on the environment or application. Another feature of this coder is that a sample of the background noise is periodically sent to the receiver. Since most voice conversations are made up of approximately 50 silence this sample can be used to recreate the background noise thus reducing the amount of data to be sent and hence increasing system capacity since no interference will be caused during the idle periods. The process uses a closed loop system that compares the sound sample of the voice with what is stored under a predicted code reference. The output from this process will represent the error between the two and is passed through a perceptual weighting device that will mimic the sensitivity of the human ear to gauge how much distortion this error will produce. After error analysis a new codebook reference may be chosen that should be a better match to the incoming speech. This closed loop should produce a very close codebook reference that can be used in the receiver to recreate the speech. The receiver will simply contain the same codebook a speech generator and a filter. The V oice tone activity detectors will handle the multiplexing of the background noise to be used in the receiver for idle periods. Discontinuous transmission bits indicate when to use this background noise.

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WCDMA Air Interface - 22 - EN/LZT 123 7279 R4A The two main advantages of using discontinuous transmission are: • Less power will be transmitted by the mobile and hence less interference which will result in an increase in capacity. • Longer mobile battery life. A/D Linear Predictive Coding LPC Filter Codebook Index Codebook Perceptual Weighting Error Analysis Speech Generator Vocoder Output Bits MUX Voice Tone Activity Detectors • Mode Indication bits • Comfort Noise • Tone Emulation • DTX Indication Σ + - Prediction Error Benefits of Activity Detection: 1 2 Figure 1-9: ACELP/AMR Voice Coding The multi-rate speech coder is a single integrated speech codec with eight source rates: 12.2 GSM 10.2 7.95 7.40 6.70 PDC 5.90 5.15 and 4.75 kbps. The AMR rates can be controlled by the radio access network. To facilitate interoperability with existing cellular networks some of the modes are the same as in existing cellular networks. The AMR is capable of switching its bit rate every 20 ms speech frame upon command. However in P2.1 only 12.2 kbps is used. The bit rate of the AMR speech connection is controlled by the radio access network depending on the air interface loading and the quality of the speech connections. During high loading such as during busy hours it is possible to use lower AMR bit rates to offer higher capacity while providing slightly lower speech quality. Also if the mobile is running out of the cell coverage area and using its maximum transmission power a lower AMR bit rate can be used to extend the cell coverage area. Adaptive multi-rate also contains error concealment. The purpose of frame substitution is to conceal the effect of lost speech frames. If several frames are lost muting is used to prevent possibly annoying sounds as a result of the frame substitution.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 23 - ERROR DETECTION AND CORRECTION - CRC AND FEC CODING In all radio systems the air interface will add noise to the signal Figure 1-10. This will produce a distortion in the received signal. In the case of an analogue cellular system the human ear perform error correction of this received signal and noise. However in digital systems we do not have this luxury. This noise will result in bit errors that is what left the transmitter as a logic 1 could be interpreted as a logic 0 if the level of noise lowers the amplitude below the threshold for a logic 0. The same could be the case for a transmitted logic 0 being interpreted as a logic 1. All digital systems must have some method of overcoming these errors. Digital Cellular Analog Cellular Transmitted Signal Received Signal + Noise Transmitted Signal Received Signal + Noise Figure 1-10: Digital Cellular Error Correction This concept can be related to addressing envelopes. The address on the left Figure 1-11 contains just enough information to get to the destination. The envelope on the right contains some unnecessary or redundant data. If both envelopes were subjected to the same amount of errors the one on the left would be undeliverable. However the redundant data in the right hand one would allow it to be delivered.

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WCDMA Air Interface - 24 - EN/LZT 123 7279 R4A A process that produces this error protection without increasing the bandwidth too much is required for cellular transmissions. Example: Mailing a letter – Extra redundant symbols in address help correct lost symbols – ZIP codes used to detect errors in the address With minimal data... Errors are uncorrectable With redundant data... Errors are correctable EM 5 Main Street Littletown Eddie McConnell 5 Main Street Littletown LT1701 Figure 1-11: Digital Cellular Error Correction Example: Mailing a letter in the US. Extra redundant symbols in address help correct symbols. ZIP codes are used to detect errors in the address. CRC Cyclic Redundancy Check CRC is used to detect if there are any uncorrected errors left after error correction. Blocks of data are passed through a CRC generator Figure 1-12 which will perform a mathematical division on the data producing a remainder or checksum. This is added to the block of data and transmitted. The same division is performed on the data block in the receiver. If a different checksum is produced the receiver will know that there is an error in the block of data alternatively there is an error in the received checksum. This knowledge is used to calculate Block Error Ratio BLER used in the outer loop power control.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 25 - The longer the checksum the greater is the accuracy of the process. In the example above the checksum was twelve bits long. Twelve bits of binary information represents 2 12 4096 different combinations. It could be imagined that various combinations of errors on the data and the checksum would produce the same checksum. The longer the checksum the less likely it is for this to happen. Checksum 12 bits 110010110011 Original Data 244 bits CRC Generator Original Data 1001011010.. CRC Generator Re-Generated Checksum 110010110001 Transmitter Receiver If Checksums do not match there is an error Received Data 1001010010.. Received Checksum 110010110011 RF Transmission Path Figure 1-12: CRC Coding WCDMA specifications Figure 1-13 specify a range of checksum lengths ranging from 0 to 24 bits. PKzip used to compress files in the computer industry uses a 32-bit checksum for greater accuracy. CRC Algorithms – 0 8 12 16 or 24 parity bits determined by upper layers gCRC24 D 24 + D 23 + D 6 + D 5 + D + 1 gCRC16 D 16 + D 12 + D 5 + 1 gCRC12 D 12 + D 11 + D 3 + D 2 + D + 1 gCRC8 D 8 + D 7 + D 4 + D 3 + D + 1 3GPP TS 25.212¶ 4.2.1.1 3GPP TS 25.212¶ 4.2.1.1 Figure 1-13 CRC Algorithms parity bits FEC The next part in the transmitter is Forward Error Correction FEC. The function of this block is to help the receiver correct bit errors caused by the air interface.

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WCDMA Air Interface - 26 - EN/LZT 123 7279 R4A One method for correcting these errors would be to send the information a number of times Figure 1-14. Provided this is more than twice the receiver could select which message is most correct by a “best out of three” decision. The more times the data is transmitted the better is the error protection. However the bandwidth is also increased proportionally What is required is a system that provides forward error correction with minimal increase in the bandwidth. Send message many times 010010110 010010110 010010110 010010110 010010110 • • • Forward Error Correction Up to 6x data expansion... But the most powerful results Figure 1-14: FEC Coding. How do you correct errors at the receiver There are two basic types of FEC available block or continuous codes. Block codes work by processing the data into unique code words. This would be similar to transmitting “New York City” to represent ‘NYC’. These redundant bits provide the error correction. As this type of system works on blocks of data it is not suitable for conversational transmissions. Continuous codes such as convolutional codes and turbo codes on the other hand are continuously produced as the data is fed to the FEC. The result will contain redundant bits that help to correct errors. WCDMA will utilize convolutional coding for low data rates where a low latency and real time processing are required as speech and signaling. All other services where latency and processing power is not a problem turbo coding may be used. This type of coding gives a much better error correction performance than traditional methods.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 27 - Convolutional coding Figure 1-15 gives a high level overview of the operation of the Convolutional coder. Original Data 00011011... FEC Generator FEC Encoded data 1010011100110110... Original Data 00011011 Viterbi Decoder Transmitter Receiver RF Transmission Path Figure 1-15: FEC Coding: The Convolutional Coder. The original data is fed to the FEC generator which in this case produces twice as much data. A coder that produces this increase that is two bits out for one bit in is known as a 1/2 rate coder. One that produces three bits of information for one input is known as a 1/3 rate coder. This output is not simply the input data repeated it will be subjected to noise superimposed by the RF transmission path. In the receiver a device known as a ‘Viterbi Decoder’ is used to correct these errors and recover the original data. This device works by taking the actual level of the data and estimating whether this was a 1 or a 0 when it left the transmitter rather than use thresholds for 1 and 0.

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WCDMA Air Interface - 28 - EN/LZT 123 7279 R4A D D Input Data 1010... MUX X 2k+1 X 2k Coder Output clock R 1/2 k2 Convolutional Coder • For every input bit there are two output bits • The maximum time delay is 2 clock cycles Figure 1-16: Convolutional Coding Example. Figure 1-16 shows how a simple Convolutional coder could be created using two shift registers two XOR gates and a multiplexer. For every input data bit there will be two output bits produced X 2k and X 2k+1 . FEC Coding: Example State 00 State 01 State 10 State 11 State 00 State 01 State 10 State 11 State Diagram 11 00 10 01 11 00 01 10 x 2k x 2k+1 Coder Output Clock Cycle Current Input Delayed Inputs Outputs D k D k-1 D k-2 X 2k X 2k+1 1 0 0 0 0 0 2 1 0 0 1 1 3 0 1 0 0 1 4 1 0 1 0 0 5 1 1 0 1 0 6 1 1 1 0 1 7 0 1 1 1 0 8 0 0 1 1 1 X 2k D k XOR D k-2 X 2k+1 D k XOR D k-1 XOR D k-2 STATE Figure 1-17: FEC Coding Example Continued. X 2k will be made up from the present input bit D k exclusive OR’d with the previous input bit D k-1. X 2k+1 will be D k exclusive OR’d with the last input bit D k-1 and the twice previous bit D k-2.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 29 - Figure 1-17 shows what these outputs will be for an input data stream of 01011100. Also shown is a state diagram for this operation. By taking the present and past bit as the input state the options for sending two bits of data is reduced from 2 2 four to only two. This is the power behind the decoder since two bits of data are used to signal the state change of the input which can only be one of two options. Convolutional coding is applied for standard services requiring BERs up to 10 -3 which is the case for voice applications. The constraint length for the proposed convolutional coding schemes is 9. Both 1/2 rate and 1/3 rate convolutional coding has been specified. Turbo Coding is required for high-quality services that require BERs from 10 -3 to 10 -4 Convolutional codes are usually described using two parameters the code rate and the constraint length Figure 1-18. The code rate k/n is expressed as the ratio of the number of bits input to the convolutional encoder k to the number of channel symbols output from the convolutional encoder n in a given encoder cycle. The constraint length parameter K denotes the length of the convolutional encoder that is how many k-bits stages are available to feed the combinatorial logic that produces the output symbols. Closely related to K is the parameter m which indicates how many encoder cycles an input bit is retained and used for encoding after it first appears as input to the convolutional encoder. The m parameter can be thought of as the memory length of the encoder. 3GPP TS 25.212¶ 4.2.3.1 3GPP TS 25.212¶ 4.2.3.1 D D D D D D D D Data In 2:1 MUX Data Out D D D D D D D D Data In 3:1 MUX Data Out Rate 1/2 k9 coder: G 0 561 8 G 1 753 8 Rate 1/3 k9 coder: G 0 557 8 G 1 663 8 G 2 711 8 Figure 1-18: WCDMA Convolutional Code Generators

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WCDMA Air Interface - 30 - EN/LZT 123 7279 R4A Viterbi decoding Viterbi decoding process Figure 1-19 can be described in the following steps: 1. Calculate Branch Metric for each possible state transition BM |R 1 - T 1 | + |R 2 - T 2 | 2 R 1 R 2 Received data values T 1 T 2 Transmitted data values 2. Calculate Cumulative Path Metric. Path Metric is the sum of “N” previous Branch Metrics N is memory depth of Viterbi Decoder. 3. Calculate surviving path. The surviving path is the path with the lowest Path Metric. 4. Extract the error-corrected data. The error-corrected data sequence is equal to the first bit of each state code along the surviving path. Viterbi Decoding Process: 1 Calculate Branch Metric for each possible state transition BM |R 1 -T 1 | + |R 2 -T 2 | 2 R 1 R 2 Received data values T 1 T 2 Transmitted data values 2 Calculate Cumulative Path Metric Path Metric is sum of “N” previous Branch Metrics N is memory depth of Viterbi Decoder. 3 Calculate surviving Path The surviving path is the path with the lowest Path Metric. 4 Extract the error-corrected Data The error-corrected data sequence is equal to the first bit of each state code along the surviving path Example: Received Signal R 1 R 2 0 1 T 1 T 2 0 0 T 1 T 2 0 1 T 1 T 2 1 1 T 1 T 2 1 1 T 1 T 2 0 0 T 1 T 2 0 1 T 1 T 2 1 0 T 1 T 2 1 0 State 00 State 01 State 10 State 11 State 00 State 01 State 10 State 11 1 0 1 1 1 4 4 0 Branch Metric Figure 1-19: Viterbi Decoder.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 31 - The Viterbi decoder is built on top of a trellis tree consisting of stages and transitions. The basic operation consists of branch metric calculations based on path selection and back-tracing. The branch metric processing involves calculation of 2 k values kconstraint length for each received bit. In the example given above k2 which leaves us with four different states. For each state there exists only two possibilities either 0 or 1. If the received signal is 01 then our initial state is either 10 and the next state is 01 or the initial state is 11 and the next state is 11. This is true since the branch metric calculation is minimal for these transitions BM0.The four possible states of the encoder are depicted as four rows of horizontal dots. There is one column of four dots for the initial state of the encoder and one for each time instant during the message. For a 4-bit message with two encoder memory flushing bits there should be six time instants in addition to t0 which represents the initial condition of the encoder. It should be clear that since the initial condition of the encoder is state 00 and the two memory flushing bits are zeroes the state starts out at state 00 and ends up at the same state. Each time we receive a pair of channel symbols we are going to compute a metric to measure the “distance” between what we received and all the possible channel symbols pairs we could have received. The first pair channel symbol can be either 00 or 11. That is because we know the convolutional encoder was initialized to the all zero state and given one input bit 1 or 0. In the second pair channel symbols branch metric is computed for four different possibilities. For each transition the branch metric result is added to the next transition result. The operation of adding the previous accumulated error metric to the new branch metric comparing the results and selecting the smallest value to be retained for the next instant is called the add-compare-select operation. Figure 1-20 shows a noise-free example where the received signal is a pure combination of 1s and 0s.

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WCDMA Air Interface - 32 - EN/LZT 123 7279 R4A 1 1 1 1 0 1 0 1 0 0 0 0 1 0 1 0 4 1 0 1 1 4 0 1 4 1 0 1 4 4 1 0 0 1 Transmitted Data: Received Data: 0 0 0 1 1 0 1 1 0 0 0 1 1 0 1 1 0 0 0 0 Path with lowest path metric has the least likelihood of error Output --- 0 1 0 1 1 Figure 1-20: Viterbi Decoding No Noise. 1 1 1.1 0.8 0 1 -.3 1.2 0 0 0.6 0.5 1 0 0.8 0.3 3.61 2.25 1.21 1.21 0.09 2.25 0.81 0.81 .25 2.25 6.25 0.25 1.21 1.21 Transmitted Data: Received Data: 0 0 0 1 1 0 1 1 0 0 0 1 1 0 1 1 .09 .34 1.55 1.80 0.81 0.81 Output --- 0 1 0 1 1 1.15 2.36 3.80 1.96 Figure 1-21: Viterbi Decoding With Noise. Figure 1-21 shows how the Viterbi decoder recovers a noisy received data signal easily. Notice that the path through the trellis of the actual transmitted message shown in bold is associated with the accumulated error metric. The decoding process begins with building the accumulated error metric for a number of received channel symbol pairs. At each step it accumulates the smallest accumulated error metric from the preceding state. Looking at step 3 in the example above the path from state 01 to 00 is smaller than the path 01 to 10 but the latter path has been chosen. This is because the actual path that determines the transmitted data signal should be pointed out after computing the branch metric up to the end of the message signal for all possible paths. Then the path with the smallest accumulated error metric value is the correct one.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 33 - Interleaving Many radio propagation effects such as reflection can attenuate the transmitted radio signal Figure 1-22. Figure 1-22: Multipath Fading. The received signal contains many time- delayed replicas. This occurs when the propagation wave reflects on an object which is large compared to the wavelength for example the surface of the earth buildings walls etc. This phenomenon is called multipath propagation and it has several effects these are: • Rapid changes in signal strength over a small area or time interval • Random frequency modulation due to varying Doppler shifts on different multipath signals. • Time dispersion caused by multipath propagation delays Multipath propagation yields signal paths of different lengths with different times of arrival at the receiver. Typical values of time delays µs are 0.2 in Open environment 0.5 Suburban and 3 in Urban.

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WCDMA Air Interface - 34 - EN/LZT 123 7279 R4A Direct Signal Reflected Signal Combined Signal Figure 1-23: Multipath Fading. The combination of direct and out-of-phase reflected waves at the receiver yields attenuated signals Figure 1-23. This attenuation can result in bit errors that occur in consecutive blocks of data. As a result the Viterbi decoder fails to recover such errors. The solution to overcome this problem is to use a block interleaving technique as shown in Figure 1-24. Time Amplitude To Viterbi decoder Original Data Samples 1 2 3 4 5 6 7 8 9 Interleaving Matrix 1 2 3 4 5 6 7 8 9 Transmitter Interleaved Data Samples 1 4 7 2 5 8 3 6 9 RF Transmission Path Interleaved Data Samples 1 4 7 2 5 8 3 6 9 Errors Clustered De- Interleaving Matrix 1 2 3 4 5 6 7 8 9 De-Interleaved Data Samples 1 2 3 4 5 6 7 8 9 Receiver Errors Distributed Figure 1-24: Block Interleaving.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 35 - A radio channel produces bursty errors. Because convolutional codes are most effective against random errors interleaving is used to randomize the bursty errors. The interleaving scheme can be either block interleaving or convolutional interleaving. Typically block interleaving is used in cellular applications. The first step of interleaving is determined by the delay requirements of the service. Speech service for example uses 20 ms of interleaving and PS 384 kbps uses 10 ms of interleaving Figure 1-25. Different services and signaling are multiplexed together on one physical channel after frame segmentation and then a second stage of interleaving is used which is always 10 ms long. Interleaving – 1st-Stage Interleaver Performed prior to service multiplexing Interleaving depth of 1 2 4 or 8 columns. 102040 or 80 ms – 2nd-Stage Interleaver Performed after service multiplexing Interleaving depth of 30 columns always 10 ms 3GPP TS 25.212 ¶ 4.2.5 4.2.11 3GPP TS 25.212 ¶ 4.2.5 4.2.11 Figure 1-25: 1 st and 2 nd Interleavers Turbo Codes Turbo Codes are newly introduced parallel recursive and systematic convolutional codes. These codes are used for channel coding and decoding in order to detect and correct errors occurring in the transmission of digital data through different channels The iterative method of the decoding scheme helps to achieve the theoretical limit near Shannon-limit in error correction performance. Each decoder uses the received data and extrinsic information which has been delivered by the preceding decoder to give decoded data and new extrinsic information. Interleaving helps the decoders to improve their correction capability by keeping the extrinsic information with the received data un- correlated. The Turbo code structure is based on a combination of two or more weak error control codes Figure 1-26.

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WCDMA Air Interface - 36 - EN/LZT 123 7279 R4A Encoder 1 Encoder 2 MUX Data Decoded Data DE- MUX Decoder 2 D P1 P2 D P1 P2 D Turbo Encoder Turbo Decoder Interleaver Interleaver Interleaver De-Interleaver Decoder 1 Figure 1-26: Turbo Coding. The data bits are interleaved between two encoders generating two parity streams. The whole process results in a code that has powerful error correction properties. A more detailed figure of the turbo coder is shown in Figure 1-27. Data In Rate X M U X Data Out 3x input bits + 12 Termination bits X k X k Z k Turbo Interleaver X’ k Z’ k At end of data block both switches go “down” to provide 12-bit Trellis Termination: x K+1 z K+1 x K+2 z K+2 x K+3 z K+3 x K+1 z K+1 x K+2 z K+2 x K+3 z K+3 3GPP TS 25.212¶ 4.2.3.2 3GPP TS 25.212¶ 4.2.3.2 D D D D D D Figure 1-27: WCDMA Turbo Code Generator Rate matching Rate matching is performed on the data to change the data rate to one that can be accommodated by the system. It should be noted that this function could not only be used to reduce the data rate by puncturing bits but also to increase the data rate by padding it with extra bits.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 37 - CHANNELIZATION CODES The main purpose of the channelization codes is to separate the data channels in the uplink and the downlink coming from the same transmitter. Note that channelization codes have many names like orthogonal short spreading and Hadamard codes. Channelization codes requires synchronization since the waveforms are orthogonal only if they are aligned in time. Figure 1-28 shows three different correlation cases using channelization codes: a Same channelization code. This means that the receiver and transmitter use identical codes with the same time offset. b Different channelization codes. c Same channelization code but with non-zero offset. Input Data +1 -1 +1 -1 +1 –1 +1 +1 –1 +1 -1 -1 +1 –1 +1 +1 –1 +1 -1 -1 +1 –1 +1 +1 –1 +1 -1 -1 +1 –1 +1 +1 –1 +1 -1 +1 –1 +1 –1 –1 +1 –1 +1 -1 +1 –1 +1 +1 –1 +1 -1 -1 +1 –1 +1 +1 –1 +1 -1 +1 +1 +1 +1 +1 +1 +1 +1 -1 -1 +1 –1 +1 +1 –1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 –1 +1 –1 –1 +1 –1 +1 +1 –1 –1 –1 +1 –1 –1 -1 Orthogonal code in Transmitter Transmitted Sequence Orthogonal Code used in Receiver 8 0 -4 Integrate Result +1 0 -0.5 Divide by Code Length Case III: Correlation using channelization codes a Same channelization code b Different channelization codes c Same code with non-zero time offset x x x Integrate Integrate Integrate x xx Transmitter Receiver Figure 1-28: Code Correlation: Correlation Using Channelization Codes. The correlation in case a is 100 and the channel is perfectly reconstructed. In case b the codes channels are perfectly separated and the correlation is 0. In case c the result is unpredictable which shows that the timing is very important to preserve the orthogonal properties of the code.

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WCDMA Air Interface - 38 - EN/LZT 123 7279 R4A Figure 1-29 shows an example of channelization coding of four data channels Channelization Code CC 1-4 used at the transmitter side. This case could represent for example the downlink where each specific channel is multiplied by a channelization code. The received signal is correlated with Channelization Code CC 3 which reconstructs data channel 3 perfectly. In this example the receiver correlates the composite received signal using Channelization Code 3. The result is a perfect reconstruction of Data Channel 3 with no interference from the other data channels. To realize this perfect cross-correlation property it is essential that the channelization codes be received in perfect timing relation to each other. CC 4 CC 3 CC 2 CC 1 RF Modulation RF Demod CC 3 Data Channel 1 Data Channel 2 Data Channel 3 Data Channel 4 Receiver Linear Addition Transmitter Figure 1-29: Channelization coding. Each data symbol of the data is XOR operated with the corresponding channelization code Figure 1-30. The length of the channelization code depends on the user data rate. After the operation the output will always end up with a rate of 3.84 Mchips/s.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 39 - User 1 Data: 1 0 1 Multiply with channelization Code 1 –1 1-1 User 1 channelization coded data: -1 1-1 1 1-1 1-1 -1 1-1 1 You send one channelization code for every data bit If you want to send a digital “0” you transmit the assigned channelization code If you want to send a digital “1” you transmit the inverted channelization code Transmitted “chips” Data Channelization code D/A conv. -1 +1 -1 Figure 1-30: Channelization Codes. The output from the XOR is the sum of each channel data stream and its corresponding CC. Figure 1-31 shows an example of four different channels being coded and sent from the same transmitter. After the channelization codes are multiplied by each channel they are added together to form a composite transmitted data stream. Data Channel 1 0 1 0 Data Channel 2 0 0 1 Multiply with CC1 1 1 1 1 Multiply with CC2 1 1-1-1 After channelization coding +1+1+1+1-1-1-1-1+1+1+1+1 ∑ Composite Transmitted Data: +2 +2 -2 +2 +2 -2 -2 -2 0 0 0 +4 Data Channel 3 1 0 1 Multiply with CC3 1–1 1-1 4-chip Channelization Code Set 1 1 1 1 1 2 1 1 -1 -1 3 1 –1 1 -1 4 1 -1 -1 1 After D/A Mapping +1 –1 +1 After channelization coding +1+1-1-1+1+1-1-1-1-1+1+1 After D/A Mapping +1 +1 –1 After channelization coding -1+1-1+1+1-1+1-1-1+1-1+1 After D/A Mapping -1 +1 -1 Data Channel 4 0 0 0 Multiply with CC3 1-1-1 1 After channelization coding +1-1-1+1+1-1-1+1+1-1-1+1 After D/A Mapping +1 +1 +1 Figure 1-31: Channelization Coding example - Transmitter. Figure 1-32 shows how the composite received data is decoded at the receiver. Notice that the properties of the channelization code are also valid for when a sum of channelization streams is decoded regardless of how much power there is in the other codes.

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WCDMA Air Interface - 40 - EN/LZT 123 7279 R4A Integrate Normalize Integrate Normalize Integrate Normalize Integrate Normalize Result: 1 -1 1 Result: 1 1 -1 Result: -1 1 -1 Result: 1 1 1 Integrate: Sum four consecutive values after multiplication with CC. Normalize: Multiply by 1 / code length “Correlation” Composite Received Data: +2 +2 -2 +2+2 -2 -2 -20 0 0 +4 Multiply with CC1 +1 +1 +1 +1 Multiply with CC2 +1 +1 -1 -1 Multiply with CC3 +1 -1 +1 -1 Multiply with CC4 +1 -1 -1 +1 Map A→D 0 1 0 Map A→D 0 0 1 Map A→D 1 0 1 Map A→D 0 0 0 4-chip Channelization Code Set 1 1 1 1 1 2 1 1 -1 -1 3 1 –1 1 -1 4 1 -1 -1 1 Figure 1-32: Channelization Coding example - Receiver. Figure 1-33 shows the usage of the channelization codes in the uplink and the downlink. CC1 CC2 CC3 CC4 CC5 CC6 CC7 CC1 CC2 CC3 CC1 CC2 CC1 CC2 CC3 CC4 Uplink: Channelization Codes used to distinguish data channels coming from each User Equipment UE Downlink: Channelization Codes used to distinguish data channels coming from each cell Figure 1-33: Uplink and Downlink Channelization Code Usage. In the downlink the channelization codes are used to separate the different data channels coming from each cell. For the dedicated channels this represents the different users since only one scrambling code is used for all downlink transmission from the cell. In the uplink the channelization codes are used to separate the different data channels sent from the UE to the each cell. The separation of the different UEs will here be done with different scrambling codes.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 41 - Figure 1-34 shows the channelization code tree. Two codes are said to be orthogonal when their inner product is zero. The inner product is the sum of all the terms we get by multiplying two codes element by element. For example 1 1 1 1 and 1 1 -1 -1 are orthogonal since 1 1 + 1 1 + 1 -1 + 1 -1 0 1 11 1-1 1111 11-1-1 1-11-1 1-1-11 1111-1-1-1-1 11111111 11-1-1-1-111 11-1-111-1-1 1-11-1-11-11 1-11-11-11-1 1-1-111-1-11 1-1-11-111-1 Digital/Analog Mapping logic 0 ↔ analog +1 logic 1 ↔ analog - 1 11-1-111-1-111-1-1 11-1-1 Figure 1-34: Channelization Code Generation. The code tree corresponds to different discrete Spreading Factor SF levels SF1 2 4 8…n 2 . Different spreading factor levels mean different code lengths and they are therefore normally referred to as Orthogonal Variable Spreading Factors OSVF. The idea is to be able to combine different messages with different spreading factors and keep the orthogonality between them. We therefore need codes of different length that are still orthogonal. Of course the chip rate remains the same for all codes so short ones will be transmitted at a higher information rate than longer ones. The longer the code is the lower will the data rate be and the other way around. The spreading factor corresponds to the length of the code and the number of channels sending at a certain bit rate. • SF: 4-512 is allowed in the WCDMA DL. • SF: 4-256 is allowed in the WCDMA UL. How much the channelization code spreads the signal depends on its variation. The scrambling codes on the other hand always have a high transition rate and will therefore always spread and affect the signal bandwidth needed.

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WCDMA Air Interface - 42 - EN/LZT 123 7279 R4A 1 11 1-1 1111 11-1-1 1-11-1 1-1-11 1111-1-1-1-1 11111111 11-1-1-1-111 11-1-111-1-1 1-11-1-11-11 1-11-11-11-1 1-1-111-1-11 1-1-11-111-1 480 kb/s 480 kb/s 480 kb/s 480 kb/s 480 kb/s 480 kb/s 480 kb/s 480 kb/s Chip Rate 3.840 Mcps Figure 1-35: Usage of the channelization code tree Figure 1-35 shows an example of the allocation of the code tree for eight users sending at the same rate of 480 kbps. Figure 1-36 below shows an example of four users sending at SF 8 and one user sending at SF 2. Chip Rate 3.840 Mcps 480 kb/s 480 kb/s 480 kb/s 480 kb/s 1 11 1-1 1111 11-1-1 1-11-1 1-1-11 1111-1-1-1-1 11111111 11-1-1-1-111 11-1-111-1-1 1-11-1-11-11 1-11-11-11-1 1-1-111-1-11 1-1-11-111-1 User with 4x Bit Rate Unusable Code Space 1.92 Mb/s Figure 1-36: Usage of the channelization code tree It should be noted that any two codes of different layers are also orthogonal except when one of the two codes is a mother code of the other. Therefore if a UE is transmitting data with 960 kbps SF4 the other branches of this mother code cannot be used any more. Figure 1-37 gives a summary of the channelization codes.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 43 - WCDMA allows multiple data streams to be sent on the same RF carrier – Perfect isolation between data streams – Timing between data streams must be exact – Maximum number of data channels Channelization code length The longer the code the slower the data rate WCDMA advantages are limited in practice – Multipath small timing errors and motion- related effects diminish the usable code space Each Data Stream has a unique Channelization Code Many users share the same frequency and time IS-95 cdma2000 WCDMA Frequency Code Division Multiple Access Data 1 Data 2 Data 3 ... Figure 1-37 Summary of Channelization Codes SCRAMBLING CODES In WCDMA each user is assigned a unique code which it uses to encode its information-bearing signal. The receiver knowing the code sequences of the user decodes a received signal after reception and recovers the original data. Spreading codes are divided into scrambling codes and channelization codes CC. Each transmitter cell in downlink is assigned a different scrambling code and each data channel is assigned different CC code. Since the bandwidth of the scrambling code is chosen to be much larger than the bandwidth of the information-bearing signal the encoding process enlarges the spectrum of the signal. The resulting signal is also called a spread spectrum signal and WCDMA is often denoted as spread spectrum multiple access. A simple analogy to explain the concept of scrambling codes is to use that of a cocktail party Figure 1-38.

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WCDMA Air Interface - 44 - EN/LZT 123 7279 R4A What do YOU hear... •If you only speak Japanese •If you only speak English •If you only speak Italian •If you only speak Japanese but the Japanese- speaking person is all the way across the room •If you only speak Japanese but the Spanish- speaking person is talking very loudly Figure 1-38: The WCDMA Cocktail Party. Imagine that you are invited to a cocktail party where the invited people speak different languages such as Japanese Russian Spanish and Italian. What would you then hear: 1. If you only speak Japanese 2. If you only speak English 3. If you only speak Italian 4. If you only speak Japanese but the Japanese-speaking person is all the way across the room 5. If you only speak Japanese but the Spanish-speaking person is talking very loudly In the first case the Japanese speaking person would understand the Japanese speaking persons and be able to follow their conversation. The other persons speaking other languages will on the other hand not be possible to understand and will only be interpreted as noise. In the second case there is no English speaking person at the cocktail party and everything will just be noise.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 45 - The third case is similar to the first with the difference that the Italian speaking person not only will understand the other Italian speaking persons but also some Spanish since there are common words in both the languages. The Spanish speaking persons can in this case be seen as interference. In case four the Japanese speaking person will have to speak higher. This corresponds to a power increase due to for example path loss when the user is further away from the base station. The final case shows a user that is using a power level that is too high. Since all the users in the system are transmitting at the same frequency at the same time they will of course be dependent on the other users output power and will be strongly interfered by the by the user sending at an output power level that is too high. This shows that power is the common shared resource and that efficient and fast power control is essential in a WCDMA system to achieve and maintain a high capacity. In TDMA during a timeslot for a particular user the base station can broadcast to the user and the user to the base station at whatever power they wish. This would be like one person shouting and everybody else staying quiet. However WCDMA is like a cocktail party with social etiquette so everybody speaks at the same time but in a low voice so people can hear the conversation they are interested in. Figure 1-39 shows an example of four transmitters. Each transmitter will use its unique scrambling code. All signals are sent over the air interface and received together at the receiver. To decode signal number 3 in the receiver scrambling code number 3 will be used. The result will be that signal number 3 is recovered and all the other signals will only become low level noise as can be seen in the right part of the figure. SC 1 RF Modulation Transmitter 1 SC2 RF Modulation Transmitter 2 SC3 RF Modulation Transmitter 3 SC4 RF Modulation Transmitter 4 RF Demod SC3 Receiver In this example the receiver correlates the composite received signal using Scrambling Code SC 3. The result is the recovered transmission from Transmitter 3 plus some spread spectrum interference from transmitters 1 2 and 4 Figure 1-39 Spread Spectrum Multiple Access

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WCDMA Air Interface - 46 - EN/LZT 123 7279 R4A What can be seen from this correlation is that if the transmitter and receiver use the same codes with the same time offset there will be a 100 correlation. What can be seen from this correlation is that if the transmitter and receiver use different codes with any time offset the correlation will only result in a low level of noise. This correlation is proportional to the inverse of the code length the scrambling code length is 38400 chips long. This is an important property of the code since the receiver will correlate the correct signal with all other signals at the same time. It is also important that this is valid with any time offset since the users in the uplink are not synchronized to each other and also for the RAKE receiver chapter 2 to handle multipath components. Figure 1-40 shows how the incoming data stream is multiplied by a scrambling code which is generated by a linear shift register with a starting sequence called a code key. If the signal were analyzed in a spectrum analyzer a main lobe and side lobes would be seen. The side lobes are not wanted and will just occupy frequency band. The signal will therefore be sent through a filter only to maintain the main lobe. In the last step after modulation the resulting signal can be seen. The properties of the signal will depend on the scrambling code characteristics and not on the initial incoming chips. Power Spectrum Magnitude dB PN Code Generator Chip Clock Fc Fd RF Modulator cosω rf t Nulls NRc F rf Filter PN Code Key ”Chips” “Chips” 0 0.1 0.2 0.3 0.4 0.5 0.6 -50 -40 -30 -20 -10 0 10 Frequency 0 0.1 0.2 0.3 0.4 0.5 0.6 -60 -50 -40 -30 -20 -10 0 10 Frequency Power Spectrum Magnitude dB 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 x 10 7 -40 -20 0 20 40 60 80 Frequency Power Spectrum Magnitude dB Figure 1-40: Why is it called spread spectrum

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 47 - If multiple users transmit a spread spectrum signal at the same time Figure 1-41 the receiver will still be able to distinguish between the users provided each user has a unique code that has a sufficiently low cross correlation with the other codes. Cross correlating the code signal with a narrow band signal will spread the power of the narrow band signal thereby reducing the interfering power in the information bandwidth. The spread spectrum signal 1 is detected together with a interference signal 2. At the receiver the spread spectrum signal 1 is despread while the interference signal signal 2 is still spread making it appear as a background noise compared to the despread signal. The power gain when decoding signal 1 can be approximated to the ratio between the chip rate and the bit rate and is called the processing gain G p . The processing gain is a result of both the spreading gain and the error protection gain.       rate Bit rate Chip Both signals “mixed” in the air interface Scrambling Code 1 Frequency Amplitude Signal 1 Scrambling Code 2 Frequency Amplitude Signal 2 Spread Spectrum Processing Gain Scrambling Code 1 Signal 1 is reconstructed Signal 2 looks like noise Both signals are received together AT THE RECEIVER... Case II: Two Transmitters at the same frequency Figure 1-41: Two Transmitters at the Same Frequency. Figure 1-42 shows a summary of the scrambling code properties.

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WCDMA Air Interface - 48 - EN/LZT 123 7279 R4A TX RX use same codes at the same time offset Scrambling Codes: 100 correlation TX RX use different codes Scrambling Codes: “Low” noise-like correlation at any time offset Average correlation level proportional to 1/code length TX RX use same codes but at different time offsets Scrambling Codes: “Low” noise-like correlation for any offset +1 chip Figure 1-42: Summary of scrambling code properties Shift register sequences are not orthogonal but they do have a narrow autocorrelation peak. The name already makes clear that the codes can be created using a shift register with feedback taps Figure 1-43. By using a single shift register maximum length sequences M can be obtained. Such sequences can be created by applying a single shift register with a number of specially selected feedback taps. If the shift register size is n then the length of the code is equal to 2-1. The number of possible codes is dependent on the number of possible sets of feedback taps that produce an M sequence. The mathematics of these generators is equivalent to the operation of ordinary algebra applied to abstract polynomials over an indeterminate X with binary valued coefficients. Each sequence is based on a generator polynomial GX b nX n + b n-1X n-1 + b n-2X n-2 +……+ b 1X 1 + 1 The uplink codes are generated using an 24-bit key and this key is given to the UE at call setup. The downlink codes are generated using an 18-bit key and these are fixed and used as needed.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 49 - • β n values are 0 or 1 determined by the specified “generator polynomial” • Maximal-length m-sequence has a repetitive cycle of 2 N -1 bits • A code of 16 777 215 bits can be replicated using only a 24-bit “key” in Uplink. In downlink a 18-bit “key” is used D D clock D D β 1 β 2 β 3 β N 1010010010001110101.. Figure 1-43: Scrambling Code Generation Figure 1-44 shows how each transmitter is assigned a different scrambling code. SC3 SC4 SC5 SC6 SC1 SC1 Cell “1” transmits using SC 1 SC2 SC2 Cell “2” transmits using SC 2 Figure 1-44: Scrambling Code Planning. A WCDMA system transmits using one frequency and the transmitter identification is determined by the scrambling codes. The cell planning does not require frequency planning as in GSM systems but requires scrambling code planning. Figure 1-45 shows a pattern of scrambling codes.

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WCDMA Air Interface - 50 - EN/LZT 123 7279 R4A SC32 SC21 SC27 SC26 SC36 SC37 SC39 SC25 SC14 SC20 SC19 SC30 SC31 SC35 SC38 SC28 SC34 SC33 SC40 SC41 SC42 SC11 SC4 SC7 SC6 SC16 SC17 SC22 SC5 SC1 SC3 SC2 SC9 SC10 SC15 SC18 SC8 SC13 SC12 SC23 SC24 SC29 N S WE Figure 1-45: Scrambling Code Planning example. The number of codes used in the downlink is restricted to 8192 in total. This is done to speed up the process for the UE to find the correct scrambling code. 512 of these are primary codes the rest are secondary codes 15 codes per primary divided into 64 code groups each group containing 8 different codes. The UE can determine which scrambling code group a cell is using by the synchronization procedure see chapter 5. Note that there are no restrictions for the number of codes generated by the 24 bits start key in the uplink case. Figure 1-46 summarize the scrambling code usage. Scrambling Code Utilization – Used to distinguish the transmission source Cell or UE in WCDMA systems Provides good but not 100 separation between multiple transmissions in the same geographic area on the same frequency – Works regardless of time-of-arrival delays – Code Planning instead of Frequency Planning Frequency Reuse 1 Limitations using Scrambling Codes – Imperfect signal separation – Not good for transmitting multiple data streams from one transmitter Each Transmitter has a unique Scrambling Code Several Transmitters share the same frequency and time Frequency Spread Spectrum Multiple Access Tx 1 Tx 2 Tx 3 ... Figure 1-46: Scrambling Code Summary Finally to summarize both the channelization and scrambling codes see Figure 1-47.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 51 - - Scrambling Codes are used: To distinguish between User Equipments in uplink To distinguish between cells – Channelization Codes are used: To distinguish between data channels coming from each User Equipment To distinguish between data channels from each cell Scrambling Codes and Channelization Codes are simultaneously utilized Frequency Code Division Multiple Access Spread Spectrum Multiple Access User 1 User 2 User 3 ... Figure 1-47: Channelization and scrambling code summary. Figure 1-48 shows how the codes are used together in a WCDMA network. 2 data channels voice control SC3 + CC1 + CC2 2 data channels 14 kbps data control SC4 + CC1 + CC2 3 data channels voice video control SC2 + CC1 + CC2 + CC3 3 data channels voice video control SC5 + CC1 + CC2 + CC3 4 data channels 384 kbps data voice video control SC6 + CC1 + CC2 + CC3 + CC4 4 data channels 384 kbps data voice video control SC2 + CC4 + CC5 + CC6 + CC7 2 data channels voice control SC1 + CC1 + CC2 1 data channels control SC1 + CC3 Voice Conversation Uplink Packet Data Videoconference Videoconference with Data Pilot Broadcast SC1 + CC P + CC B Pilot Broadcast SC2 + CC P + CC B Figure 1-48: Code usage in a WCDMA network. MODULATION A simple form of digital modulation is binary or Bi-Phase Shift Keying BPSK. The phase of a constant amplitude carrier signal moves between zero and 180 degrees. There are two possible locations in the state diagram so a binary one bipolar value –1 or zero bipolar value +1 can be sent. The symbol rate is one bit per modulation symbol. A more common type Figure 1-49 of phase modulation is Quadrature Phase Shift Keying QPSK. It is used extensively in applications including WCDMA cellular services. Quadrature means that the signal shifts between phase states which are separated by 90 degrees.

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WCDMA Air Interface - 52 - EN/LZT 123 7279 R4A Data Stream 1 “ Q ” Data Stream 2 “ I ” 90 o SUM cos wt I coswt -Q sinwt +1 -1 +1 -1 Figure 1-49: I/Q Modulation - two data streams are multiplied by a common carrier frequency but at phase offsets of 0 degrees cosine and 90 degrees sine. The signal shifts in increments of 90 degrees from 45 to 135 -45 or -135 degrees. These points are chosen as they can be easily implemented using an I/Q-modulator. Both I- and Q-branch can shift between +1 and –1 which gives two bits per modulation symbol. In the transmitter I- and Q-signals are mixed with the same local oscillator. A 90-degree phase shifter is used and the signals are separated by 90 degrees. This results that they are orthogonal to each other or in quadrature. Signals that are in quadrature do not interfere with each other. They are two independent components of the signal. I Q I 1 Q 1 I -1 Q -1 I -1 Q 1 I 1 Q -1 1 Modulation Symbol represents 2 data bits Modulation efficiency 2 bits/symbol RF Carrier amplitude RF Carrier phase angle Figure 1-50: I/Q Modulation - graphical representation of an I/Q modulated signal.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 53 - Figure 1-50 is an example of a state diagram of a Quadrature Phase Shift Keying QPSK signal. There are four states possible. It is therefore a more bandwidth-efficient type of modulation than the BPSK potentially twice as efficient. The composite signal with magnitude and phase I/Q information arrives at the receiver input Figure 1-51. The input signal is mixed with the local oscillator signal at the carrier frequency in two forms. One is at an arbitrary zero phase. The other has a 90- degree phase shift. The composite input signal is thus broken into two components an In-phase I and a Quadrature Q branch. 90 o DEMOD coswt Q coswt -I sinwt LPF LPF Data Stream 1 “ I ” Data Stream 2 “ Q ” +1 -1 +1 -1 Figure 1-51: I/Q Modulation - by multiplying the sine and cosine at the receiver the original I and Q data streams are recovered. These two components of the signal are independent and orthogonal. One can be changed without affecting the other. Normally information cannot be plotted in a polar format and reinterpreted as rectangular values without doing a polar to rectangular conversion. This conversion is exactly what is done by the in-phase and quadrature mixing processes in a digital radio. A local oscillator phase shifter and two mixers can perform the conversion accurately and efficiently. FILTERING Filtering allows the transmitted bandwidth to be significantly reduced without losing the content of the digital data Figure 1-52. This improves the spectral efficiency of the signal.

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WCDMA Air Interface - 54 - EN/LZT 123 7279 R4A RF Modulator 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -60 -50 -40 -30 -20 -10 0 10 20 Frequency Baseband filtering of data stream is required to contain RF bandwidth Figure 1-52: Data Filtering. There are many different varieties of filtering. The most common are: • Raised cosine • Square-root raised cosine • Gaussian Any fast transition in a signal whether it is amplitude phase or frequency will require a wide occupied bandwidth. Any technique that helps to slow down these transitions will narrow the occupied bandwidth. Filtering serves to smooth these transitions in I/Q modulation. On the receiver end reduced bandwidth improves sensitivity because more noise and interference are rejected. Filtering can also create Inter-Symbol Interference ISI. This occurs when the signal is filtered so that the symbols blur together and each symbol affects those around it. This level of ISI is determined by the time domain response or impulse response of he filter. A Chebyshev equiripple FIR finite impulse response filter is used for baseband filtering in CDMA systems. With a channel spacing of 5 MHz and a symbol rate of 3.84 MHz it is vital to reduce leakage to adjacent RF channels. A FIR filter means that the filter’s impulse response exists for only a finite number of samples. Equiripple means that there is a rippled magnitude frequency- response envelope of equal maxima and minima in pass-bands and stop-bands.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 55 - Figure 1-53 shows the impulse or time domain response of Chebyshev FIR filters. These filters have the properties that their impulse response rings at the symbol rate. The filter is chosen to ring or have the impulse response of the filter crossing through zero at the symbol clock frequency. 0 20 40 60 80 100 120 140 160 180 200 -2 0 2 4 6 x 10 -5 Channel Filter Digital Chebyshev 10-tap Fc 0.2Fs 0 10 20 30 40 50 60 70 80 90 100 -1 -0.5 0 0.5 1 1.5 2 Ringing may interfere with subsequent bit decisions Figure 1-53: Data Filtering Ordinary Channel Filter: Impulse Response. The sharpness of a raised cosine filter is described by alpha α. Alpha gives a direct measure of the occupied bandwidth of a system and is calculated as Figure 1-54: occupied bandwidthsymbol rate x 1+ α If the filter had a perfect characteristic with sharp transitions and an alpha of zero the occupied bandwidth would be equal to the symbol rate. In a perfect world the occupied bandwidth would be the same as the symbol rate but this is not practical. An alpha of zero is impossible to implement. At the other extreme take a broader filter with an alpha of one which is easier to implement. The occupied bandwidth in this case will be twice the symbol rate. In practice it is possible to implement an alpha below 0.2 and make good compact practical radio. WCDMA specifies alpha of 0.22.

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WCDMA Air Interface - 56 - EN/LZT 123 7279 R4A 0 50 100 150 200 250 300 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 2 sin 1 2                   − − T T T T π ω α T T T T / 1 / 1 / 1 / 1 0 π α ω π α ω π α π α ω + ≥ + ≤ ≤ − − ≤ ≤ ω H α 0.1 α 0.3 α 0.5 α 0.7 α 0.9 WCDMA uses alpha 0.22 WCDMA uses alpha 0.22 Figure 1-54: Raised-Cosine Data Filter Equations. Figure 1-55 shows the effect of alpha α on ringing effects Inter Symbol Interference. -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 α 0.01 Narrow filter α 0.3 Wide filter t1 t2 t3 t4 t5 t6 t7 t8 t9 Notes: 1 Ringing 0 at exact time instants where future data points are to be sampled 2 Low ‘alpha’ provides narrowest spectrum best for reducing adjacent channel interference 3 High ‘alpha’ provides lowest ringing amplitude best for reducing ISI 4 Theoretically even filters with very low ‘alpha’ provide zero ringing at future sample points 5 Practically low-alpha filters create greater ISI when there is timing jitter present Figure 1-55: Raised-Cosine Data Filter: Impulse Response. • Ringing 0 at exact time instants where future data points are to be sampled. • Low “alpha” provides highest ringing amplitude best for reducing adjacent channel interference. • High “alpha” provides lowest ringing amplitude best for reducing ISI.

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1 WCDMA Wireless Technology EN/LZT 123 7279 R4A - 57 - • Theoretically even filters with very low “alpha” provide zero ringing at future sample points. • Practically low-alpha filters create greater ISI when there is timing jitter present. The time response of the raised cosine filter goes through zero with a time period that exactly corresponds to the symbol spacing. At these time periods the symbol does not interfere with the adjacent symbols. One way to view a digitally modulated signal is with an eye diagram Figure 1-56. Separated eye diagrams can be generated one for the I-channel data and another for the Q-channel data. 0 50 100 150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 50 100 150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Raised Cosine Filter Chebyshev Filter Figure 1-56: Eye Diagram Comparison between Raised-Cosine Data Filter and Chebyshev Filter. Eye diagrams display I-and Q-magnitudes versus time in an infinite persistence mode with retrace. QPSK has four distinct I/Q-states one in each quadrant. There are only two levels for I and two levels for Q. The eye is open at each symbol. A good signal has wide-open eyes with compact crossover points. As the figure illustrates a filtered signal using raised cosine filter is a better signal than one filtered with a Chebyshev filter.

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2 WCDMA Power Control RAKE Receiver and Handover EN/LZT 123 7279 R4A - 59 - 2 WCDMA Power Control RAKE Receiver and Handover Objectives Upon completion of this chapter the student will be able to: • Describe the concepts of multipath reflections fading and “turn-the-corner” effects • Describe the Open-loop Inner-loop and Outer-loop power control • Describe the RAKE receiver • Describe the different handover scenarios: o Soft Handover o Softer Handover o Inter-frequency Handover o Inter-Radio Access Technology Handover

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2 WCDMA Power Control RAKE Receiver and Handover EN/LZT 123 7279 R4A - 61 - WCDMA RECEPTION ISSUES............................................................ 62 WCDMA POWER CONTROL............................................................... 63 MULTIPATH FADING............................................................................ 65 THE RAKE RECEIVER ........................................................................ 67 WCDMA HANDOVER........................................................................... 71

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WCDMA Air Interface - 62 - EN/LZT 123 7279 R4A WCDMA RECEPTION ISSUES As with all radio transmissions the WCDMA signal is subjected to multiple reflections diffractions and attenuations caused by natural objects buildings hills etc resulting in what is known as multipath propagation see Figure 2-1. This has two effects on the received signals at each end. The bit energy for a single chip is split between the various paths and arrives at different time intervals. The delay between these various arrivals is typically 1-2 µs in urban and suburban areas and up to 20 µs in hilly areas. Since the WCDMA chip rate is 3.84 Mcps the time duration of each chip is 1/3.84·10 6 0.26 µs. If the time difference in these multipath components is at least 0.26 µs the WCDMA receiver can combine these components to obtain multipath diversity. How this is achieved is explained later in the chapter. For certain time delay positions there are usually many paths virtually equal in length along which the radio signal travels. For example when two paths have a length difference of half a wavelength 7 cm at 2 GHz they will cancel each other out. This type of fading is known as fast or Rayleigh fading and takes place even as the receiver moves across short distances. Figure 2-1: Multipath fading

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2 WCDMA Power Control RAKE Receiver and Handover EN/LZT 123 7279 R4A - 63 - WCDMA POWER CONTROL Power control is necessary in any spread spectrum system to ensure that each user transmits and receives just about the right amount of power to maintain the connection quality while at the same time causing as little interference as possible to other users. For optimum performance the power control must be fast so that the variations caused by the rapidly changing radio environment can be followed. The dynamic range must in the case of the UL be very large since a UE close to a base station may well experience a pathloss that is 60-80 dB lower than a UE at the cell border. It is crucial to combat this so-called near-far effect. In the uplink the base station measures the received Signal-to- Interference Ratio SIR and compares this to a target SIR. If the measured SIR is below the target then the base station requests the mobile to increase its power and vice versa. This type of power control is known as the Inner-loop power control and is capable of adjusting the transmit power in steps of for example 1 dB at a rate of 1500 times per second. Inner-loop power control is only applicable for connections on dedicated channels. Two other types of power control are also used in WCDMA they are Outer-loop and Open-loop. Outer-loop power control is used to adjust the target SIR in reaction to changes in the block error ratio BLER after decoding. If the BLER increases then the target SIR is increased in an attempt to reduce the BLER. This process continuously changes the target SIR to maintain a minimum acceptable BLER. Outer-loop power control is only applicable for connections on dedicated channels. Open-loop power control is used to provide an initial power setting at the beginning of a connection that is when the UE/base station transmits on common channels RACH/FACH and during the initial transmission on a dedicated channel until the inner-loop is established. This is necessary since a UE transmitting a strong signal close to a base station could produce enough interference to cause dropped calls. The UE estimates the minimum transmit power required by calculating the path loss from the received signal strength and the information about the base station’s output power which is part of the system information read from the broadcast channel. If the UE receives no response from the base station at the estimated power it will retry at a slightly higher

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WCDMA Air Interface - 64 - EN/LZT 123 7279 R4A power until an acknowledgement is received. Open-Loop Power Control Compute Initial Transmit Power Measure received power from RBS Read RBS transmit power from Broadcast Channel Transmit Access Preamble Access Acknowledged Increase Transmit Power by X dB No Yes UE Begins Uplink DCH Transmission Outer-Loop slow Power Control Inner-Loop fast Power Control BLER Acceptable Raise Rx Power Target Lower Rx Power Target No Yes Received power target Increase UE Transmit Power by e.g. 1 dB Decrease UE Transmit Power by e.g. 1 dB No Yes Figure 2-2: WCDMA Power Control loops. Figure 2-2 gives an overview of the three power control algorithms from the UE transmit power perspective. During connection setup the UE makes access attempts known as access preambles at increasing power levels until the base station’s receive power target is achieved. The base station acknowledges the reception of these access preambles using the acquisition indication channel AICH. The UE then sends the message on the RACH. If a dedicated channel is set up the inner and outer loops are used to maintain the quality of the radio link. The output power of the UE is then adjusted at a rate of 1500 times per second. Figure 2-3 shows this process in a different way. The change in the power target becomes visible some time after the dedicated channel has been established due to a change in the SIR target which is triggered by the Outer-loop.

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2 WCDMA Power Control RAKE Receiver and Handover EN/LZT 123 7279 R4A - 65 - Inner-loop power control Initial receive power target RBS Receive Power Target Open-loop Power Control Access Preambles Outer-loop power control Updated receive power target of inner-loop RBS Receive Power time 800 updates/sec IS-95 cdma2000 1500 updates/sec WCDMA The PRACH is “power controlled” by means of preamble ramping i.e. UL open loop PC Preambles DPCH RACH Figure 2-3: Example of the Open-loop Inner-loop and Outer-loop. MULTIPATH FADING Fast Rayleigh fading is related to the carrier frequency the geometry of multipath vectors and the vehicle speed. As a rule of thumb there are up to four fades per second for each kilometer per hour of travel. For example a mobile traveling at 10 km/h experiences approximately 40 fades/s. As can be seen in Figure 2-4 the signal at the receiver is less than ideal and therefore makes error-free reception of data bits very difficult. The methods used to overcome fading in WCDMA are as follows: • Strong coding convolutional or Turbo and interleaving are used to recover any bit errors at the receiver this was explained in the previous chapter. However this on its own is not enough. • The Rake receiver is used to combine the energy of the most significant multipath components. • Inner-loop power control is used to overcome the fast Rayleigh fading.

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WCDMA Air Interface - 66 - EN/LZT 123 7279 R4A In essence the WCDMA receiver should be able to identify the time delay position at which significant energy arrives and assign a separate receiver to each multipath component. This is the job of the RAKE receiver each separate receiver is called a Rake finger. The output from the fingers should be combined to produce a result that is unaffected by the fading experienced in the air interface. However this is not realistically possible and so CRC FEC and interleaving performed at the transmitter is also required to enable the receiver to correct any subsequent bit errors. time mSec Composite Received Signal Strength Time between fades is related to • RF frequency • Geometry of multipath vectors • Vehicle speed: Up to 4 fades/sec per kilometer/hour Deep fade caused by destructive summation of two or more multipath reflections msec Figure 2-4: Fast Rayleigh fading.

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2 WCDMA Power Control RAKE Receiver and Handover EN/LZT 123 7279 R4A - 67 - THE RAKE RECEIVER Figure 2-5 shows a simplified block diagram of a Rake receiver. As you can see a number of Rake fingers containing correlators are used to track the different multipath reflections from one scrambling code. The outputs from the fingers are fed into a combiner. One of three different types of combining processes is employed to produce an output that is the sum of the individual mulitpath components. In order to achieve this tracking each finger simply correlates the signal with the same scrambling code but at a different phase shift. Since this is similar to using a different code a finger could quite easily be used to track another base station. This is exactly what happens in the case of Soft or Softer handovers which are explained later. The output from one finger is not fed into the combiner. This finger correlates the received signal with the scrambling code of known neighboring base stations in order to measure their power. This information is used to determine when to perform handovers. This finger is known as the “Searcher Finger”. Finger 1 Finger 2 Finger N Searcher Finger Combiner Sum of individual multipath components Power measurement of Neighboring Base Stations Figure 2-5: The RAKE receiver architecture. To make it possible for the Rake receiver to track these various components it must have some way of measuring the signal levels and phases. This is achieved by the base station transmitting known pilot symbols in the transmitted data. The Rake receiver looks for these bits and uses them to determine the phase and signal strength of each component.

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WCDMA Air Interface - 68 - EN/LZT 123 7279 R4A Each cell transmits a separate pilot channel see Figure 2-6 which is used by the searcher finger in the soft handover process to determine the signal strength received from different base stations. A data stream of all 0s is multiplied by channelization code 0. The resulting output is split and spread by the scrambling code before being passed to an I/Q modulator. The whole process is equivalent to continuously transmitting the cell’s scrambling code. This 38400 chips code is repeated every 10 ms since the WCDMA chip rate is 3.84 Mchips/s. As the base station scrambles all its transmissions with the same scrambling code this channel also serves as a phase reference for all other downlink channels. This type of spreading is known as complex spreading as the scrambling code is applied on both the I- and Q-branch. Pilot Channel Output FIR Filter FIR Filter I/Q Modulator ‘I’ PN Code ‘Q’ PN Code Orthogonal Code 0 Data All 0’s Figure 2-6: The WCDMA Common Pilot Channel CPICH. Figure 2-7 shows a more detailed diagram of a WCDMA receiver showing where the RAKE receiver fits in. The input RF signal is passed through a bandpass filter and demodulated into the I and Q components. The components are then fed to the automatically tunable delays of the various Rake fingers. These delays will compensate for the delay of the various mulitpath components of the transmitted signal. To adjust the delay of these elements the signal is correlated with the internally generated scrambling code the I and Q branches are recombined and correlated with the pilot channelization code.

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2 WCDMA Power Control RAKE Receiver and Handover EN/LZT 123 7279 R4A - 69 - Since the code is all 0s this last step can be ignored resulting in a correlation output that depends on the time difference between the internal scrambling code and that of the received signal. The delays are adjusted until a correlation peak is obtained. At this delay this so-called “sliding correlator” is said to be locked to one of the multipath components of the received signal. With this delay all other components produce low level noise. The channelization code of the desired data channel can then be used to recover the wanted channel. The other fingers of the Rake receiver carry out the same process but locking to other multipath components. The result is that each finger re-produces the original data with some interference. The finger outputs can then be combined and sent to the de-interleaver decoder and for CRC verification. BPF LPF “I” PN Code +1/-1 “Q” PN Code +1/-1 Σ Orthogon al Code +1/-1 Integrate over ‘SF’ chips De- Interleave Data Viterbi/ Turbo Decoder CRC Verification Decoded Output Bits Error Indication cos2πf RF t Pilot Orthogonal Code all zeros Timing Adj. bit rate chip rate / SF cos2πf IF t Carrier Frequency Tracking Loop Other Rake Receiver Finger Σ Rake Receiver “Finger” D D I/Q Demo d Correlator Figure 2-7: WCDMA RAKE receiver architecture. Figure 2-8 illustrates the time alignment process. In this example the composite received signal is made up of three multipath components at different time delays and amplitudes. This signal is fed to the various delays which will be centered on one of the multipath components. After correlation the original data plus interference is re-produced. The output from the fingers can then be constructively combined since the phase difference between the multipath components has been removed. The combined output is then fed to the Viterbi decoder.

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WCDMA Air Interface - 70 - EN/LZT 123 7279 R4A The accuracy of the delay needs to be ±½ chip. The total delay range must be able to cope with the maximum delay between components which can be 1 to 2 µs in an urban or suburban area to 20 µs in hilly or rural areas. Most Rake receivers can cope with a delay up to 30 µs. Three different types of combining can be performed depending on where the Rake receiver is used. If Equal-gain combining is employed then all the components are simply added together. Maximum-likelihood maximum ratio combining will apply a weighting to each result depending on the probability of that result being correct before they are combined. Alternatively the strongest signal can be selected in which case all others are discarded. 0 50 100 150 200 250 300 350 400 -2 0 2 4 6 8 10 12 14 16 18 0 50 100 150 200 250 300 350 400 -2 0 2 4 6 8 10 12 14 16 18 0 50 100 150 200 250 300 350 400 -2 0 2 4 6 8 10 12 14 16 18 n ⋅1/2-chip delay ∑ To Viterbi Decoder Composite Received Signal Scrambling Channelization Codes m ⋅1/2-chip delay k ⋅1/2-chip delay A i A i A i Correlator Correlator Correlator Equal Combining ML Combining or Select Strongest time 0 50 100 150 200 250 300 350 400 -2 0 2 4 6 8 10 12 14 16 18 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 + Interference + Interference + Interference Figure 2-8: RAKE receiver. Example of the alignment process.

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2 WCDMA Power Control RAKE Receiver and Handover EN/LZT 123 7279 R4A - 71 - WCDMA HANDOVER The connection quality has to be maintained as the User Equipment UE moves between cells. This is the purpose of the handover function. In a WCDMA system handover is performed through Soft/Softer Handover Inter-Frequency Handover Inter-Radio Access Technology Inter-RAT Handover and Inter-RAT Cell Change. Soft/Softer Handover provides the UE with the ability to add remove and replace radio links with the same frequency. In Soft Handover the UE is connected to more than one Radio Base Station RBS simultaneously. At least one radio link is always active and there is no interruption in the dataflow during the actual handover. The signals are received in the UE and combined in the RAKE receiver to give protection against fading. In Softer Handover the UE communicates with one RBS through several radio links the Softer Handover is a handover between two or more cells of the same RBS. Inter-Frequency Handover takes place when the UE makes a Handover HO to another WCDMA frequency. This is a form of hard handover. The Inter-RAT Handover function preserves signal quality on dedicated channels for circuit switched services when the UE is moving from a WCDMA network to a GSM network and vice versa. This is also a form of hard handover. The Inter-RAT Cell Change function preserves signal quality on common and dedicated channels for packet switched services when the UE is moving from a WCDMA network to a GPRS network and vice versa. Inter-RAT Cell Change is either network initiated for dedicated channels or UE initiated for common channels. No resources are reserved in the target cell before the cell change is executed. During Inter-Frequency Handover Inter-RAT Handover and Inter- RAT Cell Change the UE has only one radio link active at a time. During hard handover or cell change the connection is broken off for a short period between removal of the old radio link and establishment of the new.

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WCDMA Air Interface - 72 - EN/LZT 123 7279 R4A WCDMA systems must use soft or softer handover to reduce interference caused by near-far problems resulting from UEs at cell borders. Figure 2-9 shows the effect of not using soft handover in a WCDMA system. As the UE moves away from RBS 1 towards RBS 2 the signal received at RBS 2 may exceed its received power target and cause excessive UL interference in that cell. Since the UE is not connected to RBS 2 the base station has no way of reducing the transmit power of the UE. This excessive UL interference at RBS 2 could ultimately lead to dropped connections in RBS 2. Once the connection undergoes a hard handover to RBS 2 power control messages from RBS 2 can be used to reduce the UE transmit power and therefore reduce the interference. time Trouble zone: Prior to Hard Handover the UE causes excessive interference to RBS2 RBS2 Receive Power Target UE responding to RBS1 power control bits UE responding to RBS2 power control bits time RBS1 Receive Power Target Figure 2-9: WCDMA without soft handover Soft and softer handovers allow the UE to be power controlled by both base stations which eliminates this excessive interference see Figure 2-10.

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2 WCDMA Power Control RAKE Receiver and Handover EN/LZT 123 7279 R4A - 73 - " One finger of the RAKE receiver is constantly scanning neighboring Common Pilot Channels. " When a neighboring Common Pilot Channel reaches the t_add threshold the new RBS is added to the active set " When the original RBS reaches the t_drop threshold originating RBS is dropped from the active set Monitor Neighbor cell Pilots Add Destination RBS Drop Originating RBS Figure 2-10: Soft handover Figure 2-11 shows the received signal to interference ratio E c /N o against time for three cells. The various ‘t_add’ and ‘t_drop’ thresholds can clearly be seen. The whole process of moving from being connected to cell 1 only through soft handover with cell 1 and 2 to soft handover with cell 2 and 3 to finally being connected to cell 3 only is clearly seen. Note that hard handover usually takes place a couple of dBs inside the equal signal strength border due to a hysteresis value used to avoid ping-pong handover whereas in soft handover the addition of a new radio link occurs a couple of dBs outside the equal signal strength border. Cell 1 Connected Add Cell 2 Replace Cell 1 with Cell 3 time Drop Cell 3 E C / N 0 Cell 1 Cell 2 Cell 3 T_ADD T_REPLACE ∆t ∆t ∆t T_DROP Figure 2-11: Example of a soft handover with max active set of 2 cells. In Figure 2-12 it can be seen how both base stations control the connection during soft handover thus reducing the problem of UL interference.

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WCDMA Air Interface - 74 - EN/LZT 123 7279 R4A time RBS2 Receive Power Target 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 UE responding to RBS1 power control commands UE responding to RBS2 power control commands time RBS1 Receive Power Target 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 RBS1 RBS2 Action 0 0 Reduce power 0 1 Reduce power 1 0 Reduce power 1 1 Increase power UE responds to power control commands from both RBS1 and RBS2 Figure 2-12: WCDMA with soft handover. While connected to RBS1 only the UE acts on power control commands from that base station alone which maintains the receive power target for that cell. As the UE moves closer to RBS2 there will come a point when the threshold ‘t_add’ is exceeded and RBS2 is added to the active list. From this point on the call is said to be in soft handover. The UE is now responding to power control messages from both base stations. However it initially ignores the power increase commands from RBS 1 but responds to the power decrease commands from RBS 2. In fact the UE will only increase its power when requested to do so by BOTH base stations and will reduce its power when requested by EITHER base station. In the example the “control” of the output power of the UE is effectively changing back-and-forth between the two base stations. UEs in soft handover will cause less interference in the system and the more cells involved in the handover the lower the interference. This is why soft handover is said to improve capacity since lower UL interference results in an increased UL air interface capacity. The effect on the downlink capacity is not as clear-cut because although there is some macro diversity gain meaning that the UE on average will ask for less power then compared to a case where it is only connected to one base station there are still two downlinks that have to be transmitted on. Some key points to remember about Soft Handover are as follows: 1. Scrambling codes are used to distinguish all transmitters in a WCDMA system.

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2 WCDMA Power Control RAKE Receiver and Handover EN/LZT 123 7279 R4A - 75 - 2. Fast power control is required to sustain SSMA performance. 3. When fast power control is used soft handover is essential to avoid excessive interference during handover and it allows the UE to operate with minimum power consumption. 4. Soft handover provides performance benefits: a. “Seamless” coverage at cell borders b. Handover may be less noticeable to the user c. Increases apparent system capacity when the system is lightly loaded. 5. Soft handover also degrades system capacity. It uses redundant physical layer resources from adjacent or overlapping cells.

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3 Capacity Considerations EN/LZT 123 7279 R4A - 77 - 3 Capacity Considerations Objectives Upon completion of this chapter the student will be able to: • Explain cell reuse and code planning • Explain the issues concerning WCDMA cell planning • Explain WCDMA cell capacity considerations • Explain uplink capacity of WCDMA systems

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3 Capacity Considerations EN/LZT 123 7279 R4A - 79 - Contents CELL PLANNING ................................................................................. 80 FDMA/TDMA...................................................................................................80 WCDMA ..........................................................................................................81 UPLINK CAPACITY.............................................................................. 84 CAPACITY MANAGEMENT................................................................. 88 ADMISSION CONTROL .................................................................................88 CONGESTION CONTROL .............................................................................89

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WCDMA Air Interface - 80 - EN/LZT 123 7279 R4A CELL PLANNING This chapter highlights the fundamental aspects of WCDMA cell planning and the differences between FDMA TDMA and WCDMA systems from a cell planning point of view. FDMA/TDMA Cellular systems built on Frequency Division Multiple Access FDMA or Time Division Multiple Access TDMA are based upon the reuse of a set of carriers which is obtained by dividing the area requiring coverage into many smaller areas cells which together form clusters. This is referred to as frequency reuse planning and is important since it impacts network capacity and performance. A cluster is a group of cells within which all available carriers have been used once. Since the same carriers are used in cells in neighboring clusters interference may become a problem. The frequency reuse distance that is the distance between two sites using the same carrier must be kept as large as possible to help prevent interference. However from a capacity point of view the distance must be kept as small as possible. Cellular systems are often interference-limited rather than signal-strength limited. Figure 3-1 below shows how frequency reuse patterns of 7/21 4/12 and 3/9 are achieved. The 7/21 reuse pattern with much higher distances is used for FDMA systems like AMPS and TACS which are more sensitive to interference. The reuse patterns recommended for TDMA systems like GSM are the 4/12- and the 3/9-patterns. Today even tighter reuse can be used like 1/3 and 1/1. These patterns need features improving the interference level. 1 2 3 7 8 9 16 17 18 19 20 21 4 5 6 1 2 3 13 14 15 16 17 18 19 20 21 4 5 6 1 2 3 10 11 12 13 14 15 16 17 18 19 20 21 1 2 3 7 8 9 10 11 12 13 14 15 16 17 18 1 2 3 7 8 9 10 11 12 13 14 15 4 5 6 1 2 3 7 8 9 10 11 12 19 20 21 4 5 6 1 2 3 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 4 5 6 Reuse Pattern 7/21 B1 B2 B3 C1 C2 C3 A1 A2 A3 B1 B2 B3 C1 C2 C3 A1 A2 A3 B1 B2 B3 C1 C2 C3 A1 A2 A3 B1 B2 B3 A1 A2 A3 B1 B2 B3 C1 C2 C3 A1 A2 A3 C1 C2 C3 B1 B2 B3 C1 C2 C3 A1 A2 A3 B1 B2 B3 C1 C2 C3 A1 A2 A3 B1 B2 B3 C1 A1 A2 A3 D3 D2 D1 A1 A2 A3 D3 D2 D1 A1 A2 A3 D3 C2 C3 B1 B2 B3 C1 C2 C3 B1 B2 B3 C1 C2 C3 B1 B2 B3 D3 D2 D1 A1 A2 A3 A1 A2 A3 D3 D2 D1 A1 B2 B3 C1 C2 C3 B1 B2 B3 D3 D2 D1 C1 C2 C3 B1 B2 B3 C1 C2 C3 A1 A2 A3 D3 D2 D1 A1 A2 A3 D3 D2 D1 A1 A2 A3 D3 Reuse Pattern 3/9 Reuse Pattern 4/12 Figure 3-1: Frequency reuse patterns of 7/21 4/12 and 3/9.

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3 Capacity Considerations EN/LZT 123 7279 R4A - 81 - The output power levels must also be planned in order to maintain the signal to interference ratio C/I necessary for maintaining connections in the network for the specific frequency reuse pattern. The 4/12 reuse pattern typically used for the BCCH carrier is compatible with the planning criterion C/I 12 dB. A shorter reuse distance typically used for TCHs resulting in a smaller C/I ratio is used in the 3/9 pattern. This pattern which has higher channel utilization is only recommended if frequency hopping is implemented. That is it is compatible with the planning criterion C/I 9 dB. WCDMA This section looks at cell planning and capacity considerations for WCDMA. In a WCDMA system all users operate on the same frequency at the same time. Therefore there is no need to perform frequency reuse planning instead scrambling code planning Figure 3-2 is required. This type of planning is called code reuse planning. SC32 SC21 SC27 SC26 SC36 SC37 SC39 SC25 SC14 SC20 SC19 SC30 SC31 SC35 SC38 SC28 SC34 SC33 SC40 SC41 SC42 SC11 SC4 SC7 SC6 SC16 SC17 SC22 SC5 SC1 SC3 SC2 SC9 SC10 SC15 SC18 SC8 SC13 SC12 SC23 SC24 SC29 N S WE WCDMA Frequency Reuse: 1 Scrambling Code Reuse: 512 Codes available for code planning: 512 WCDMA: Figure 3-2: WCDMA Code Planning. In WCDMA 512 primary with 15 extra secondary per primary different codes are used.

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WCDMA Air Interface - 82 - EN/LZT 123 7279 R4A The main limiting factors for the uplink and the downlink are different. In the downlink all UEs in a cell share a single transmit power budget. Each UE has to receive a certain C/I level for the specific service to achieve the correct Quality of Service needed. The number of users in the downlink therefore depends on their location in the cell. A user that is far away from the base station will typically require more power than a user close to the base station. Noise is not the fundamental problem in WCDMA it is instead interference due to the cross correlation properties of scrambling codes which produces noise-like interference. In comparison to a traditional TDMA system the coverage of WCDMA depends on the traffic load in the cells. The more traffic the more interference and the shorter the distance must be between the RBS and the UE. In a system where the traffic load changes this will cause the cells to grow and shrink with time. This effect is often referred to as cell breathing. Interference from other base stations affects the capacity in the downlink. Despite the fact that downlink channels within one cell are orthogonal at the TX reference point they may not be orthogonal at the receiving end therefore causing noise-like interference. In the uplink all UEs have their own power budget. Interference is an important factor in the uplink as there are many UEs. Depending on the situation it is the uplink or the downlink that is the limiting factor for the WCDMA system see Figure 3-3.

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3 Capacity Considerations EN/LZT 123 7279 R4A - 83 - Cell 1 Cell 2 UE1 UE2 UE3 Cell 1 cannot accommodate UE3 because: Cell 2 cannot accommodate UE2 because: Figure 3-3: Uplink and downlink capacity limitations. In the first scenario cell 1 cannot accommodate UE3 because the increase in interference in the uplink by adding this connection would be too great and there would be a high risk of dropping a user. In this example the uplink interference has limited the capacity of the cell. In the second scenario we can see that Cell 2 cannot accommodate UE2 because it is using all its available power resources to maintain the connections to the other UEs. In other words the base station has not enough power left to achieve the required signal strength C/I required by UE2. Another way to understand this is to imagine that the base station has a total power output of 20 W. It allocates 5 W to broadcasting common channels and leaves 15 W available for traffic. In this instance it requires 2 W for each of the 5 ongoing connections and so has no power available to accommodate UE2. In this example the capacity is limited by the downlink.

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WCDMA Air Interface - 84 - EN/LZT 123 7279 R4A UPLINK CAPACITY Only the uplink capacity will be considered in this chapter. Interference is the main factor in the uplink and can be expressed as see Figure 3-4 below: I total I intra cell +I other +N th 1 I total Received Total Wideband Power RTWP total received power in signal bandwidth. I intra cell total received power from UEs in own cell I other I inter cell +I inter system total power received from UEs from other cells + interference from other sources such as adjacent frequencies and GSM Figure 3-4: WCDMA Uplink Interference If we make a single cell analysis and assume that I other 0 ⇒ I total I intra cell +I thermal noise 2

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3 Capacity Considerations EN/LZT 123 7279 R4A - 85 - If we consider the uplink capacity for a cell with one user the desired signal will only be present after correlation however as other users are added they will produce increasing levels of interference Figure 3-5. In this example there are eight users and seven of these represent interference. Interfering Signals Desired Signal Figure 3-5: Uplink Capacity Limit due to interference. Assuming that all users are perfectly power controlled and that they are using the same service i.e. are achieving the same C/I target the following is true: 3 1 int − ⋅ M C I racell Where C is the Received Signal Code Power RSCP and M is the number of users in this cell. At the receiver the C/I criterion γ must be fulfilled: ⇒ ≥ + − ⋅ + γ th th racell tot N M C C N I C I C 1 int 4 1 1 − − ≥ M N C th γ γ As can clearly be seen 1 − ⋅ M γ must be less than 1 which means that pole M M + γ 1 1. The uplink pole capacity M pole is a theoretical upper limit for the number of UEs that a cell can support giving no coverage. γ is of course service dependent and also depends on the environment and other factors. However for the purpose of this derivation it is assumed that it is a constant. For more realistic M pole values it is also possible to take for example channel activity into account if a channel is not transmitting it does not create interference for the other users.

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WCDMA Air Interface - 86 - EN/LZT 123 7279 R4A Note that as the number of users M increases the total interference level increases and this can be seen as a noise rise. It is this increase in noise that the UL must overcome to produce a sufficient C/I. Hence the higher the noise rise the lower is the coverage. The noise rise can be expressed as: 5 1 1 pole th total M M N I − Therefore when the number of users increases the noise rises and the coverage is reduced. The factor M/M pole can be seen as the load in the cell. A reasonable load in the uplink is around 50. As mentioned the C/I target γ depends on a number of factors. For speech it is typically of the order of 0.0126 i.e. –19 dB. Hence the pole capacity not taking channel activity and other effects into account is around 80. With 40 users 50 load the noise rise is then 2 +3 dB that is with 40 users the UL cell border has moved 3 dB closer to the site compared to a case with no users. In a multi-cell analysis the interference produced by users in other cells must also be taken into account as well as possible interference from other systems if present. There are many factors that influence WCDMA capacity. Factors that increase capacity include the following: • DTX gain in the speech example the DTX is 50 giving an increase in the number of users. • Cell sectorization: This refers to dividing an Omni cell into several sectors thus allowing more power to be devoted to each sector and hence increasing capacity. It also effects the inter-cell interference properties of the multi-cell network. • Antenna gain: An increase in antenna gain reduces the power output required from both the mobile and base station and hence increases capacity. • Antenna diversity: Using antenna diversity will improve the signal to noise/interference ratio of connections and hence increases capacity. • Soft handover increases capacity by allowing the mobile to make use of macro diversity in the same way as antenna diversity improves capacity.

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3 Capacity Considerations EN/LZT 123 7279 R4A - 87 - • By using higher strength error protection turbo coding the required C/I can be reduced and capacity increased. • Statistical multiplexing Factors that decrease capacity include the following: • Interference received from UEs in other cells and interference from other sources such as adjacent frequencies and GSM frequencies. • Imperfect power control resulting in some near-far interference in the uplink. • Downlink interference from other base stations. • Absorption body terrain structural atmospheric and so on that is anything that will attenuate the signal and hence increase the required output power will reduce capacity. • Use of lower strength error protection. A lower strength error protection is used to reduce the extra bits added and therefore accommodate higher data rate channels Since this will require a better C/I value the result will be a reduction in capacity. • Multipath fading. This will have an effect on the received C/I.

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WCDMA Air Interface - 88 - EN/LZT 123 7279 R4A CAPACITY MANAGEMENT Capacity Management aims to control the load in the WCDMA RAN. The purpose of Capacity Management is to maximize the capacity in WCDMA RAN while maintaining the requested Quality of Services and coverage and stabilizing the cell carrier behavior in the air interface. Capacity Management is useful in an overload situation. An overload situation occurs due to fluctuations in the uplink interference and/or the used downlink power. These fluctuations are a natural process caused by a number of factors including fading intercell interference and variations in the carried traffic of the individual connections. ADMISSION CONTROL The purpose of Admission Control is to selectively deny access request in order to limit the load and so avoids excessive triggering of congestion control. Normaly Admission Control is applied at cell level on dedicated radio link setup addition or modification where additional resources are required. The resources are a selected subset of the total resources in the RAN whose usage is constantly monitored by Admission Control Figure 3-6. In the situations of high load the input for admission about resources causes Admission Control to block new requests. Max planned interference Max planned load Noise floor Uplink interference Load New users blocked above this point User added Coverage Figure 3-6: Capacity Management Admission Control.

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3 Capacity Considerations EN/LZT 123 7279 R4A - 89 - CONGESTION CONTROL The purpose of Congestion Control is to solve overload situations. An overload situation occurs due to for example fluctuations in the UL in interference and/or the used DL power. Congestion Control is applied at cell level and becomes active when the current cell load exceeds predefined limits. The activation of Congestion Control results in a set of actions on the admitted services in a cell to reduce the cell load. Congestion Control reduces the load until it is back to an acceptable level.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 91 - 4 WCDMA Physical Layer Objectives Upon completion of this chapter the student will be able to: • Describe the 3GPP Standardization Committee and specification structure • Explain the concepts of logical transport and physical channels • Explain details of the WCDMA physical layer. • Explain the different aspects of the WCDMA downlink • Explain the different aspects of the WCDMA uplink

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 93 - CONTENTS 3GPP..................................................................................................... 94 WCDMA OSI MODEL .....................................................................................99 WCDMA DOWNLINK ......................................................................... 102 LOGICAL CHANNELS ..................................................................................104 TRANSPORT CHANNELS ...........................................................................104 PHYSICAL CHANNELS................................................................................105 CHANNELIZATION CODE INDEX ...............................................................106 COMMON PILOT CHANNEL........................................................................107 PRIMARY COMMON CONTROL PHYSICAL CHANNEL AND SYNCHRONIZATION CHANNEL .................................................................107 SECONDARY COMMON CONTROL PHYSICAL CHANNEL ......................108 PAGING INDICATOR CHANNEL .................................................................109 DEDICATED PHYSICAL CONTROL AND DATA CHANNEL.......................110 MULTIPLEXING............................................................................................115 WCDMA UPLINK.................................................................................119 DEDICATED PHYSICAL CONTROL AND DATA CHANNEL.......................120 RANDOM ACCESS CHANNEL ....................................................................123 MULTIPLEXING............................................................................................123 HPSK MODULATION ...................................................................................125

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WCDMA Air Interface - 94 - EN/LZT 123 7279 R4A 3GPP The Third Generation Partnership Project 3GPP was founded on the 4th of December 1998 to accelerate IMT-2000 standardization activities. This powerful group is responsible for producing standards for third generation systems. It currently consists of the following standardization bodies: • European Telecommunications Standardization Institute ETSI • Japanese Association of Radio Industries and Business ARIB • American National Standards Institute ANSI T1 • Telecommunications Technology Association TTA • Telecommunications Technology Committee TTC • China Wireless Telecommunication Standards CWTS. The diagram below see Figure 4-1 shows how the 3GPP is divided in to various Technical Specification Groups. The TSG- RAN group is responsible for producing specifications that relate to the air interface. There are also groups responsible for the Core Network Terminals Services and System Aspects and GSM EDGE radio access network standards. Working documents and specifications can be downloaded from the website: www.3GPP.org 3GPP Project Coordination Group ETSI ARIB T1 TSG-RAN WG 1 Layer 1 WG 2 Layers 23 WG 3 Iub Iur Iu UTRAN OM WG 4 BS Testing Protocol TSG-CN TSG-T WG 1 MS Testing WG 2 MS Services WG 3 USIM TSG-SA WG 1 Services WG 2 Architecture WG 3 Security WG 4 Codec WG 5 Telecom TSG-GERAN WG 1 Radio Aspects WG 2 Protocol Aspects WG 3 BS testing and OM WG 4 Terminal testing-RA WG 5 Terminal testing-PA WG 1 MM/CC/SM WG 2 CAMEL/MAP WG 3 Interworking WG 4 MAP/GTB/BCH/SS WG 5 OSA

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 95 - Figure 4-1: Third Generation Partnership Project 3GPP Some of the standardization documents produced by this group and relevant to this course are shown in Figure 4-2. The most important of these documents are the 25-series documents. WCDMA UTRAN Network 3GPP TS 25.401-v410: UTRAN Overall Description 3GPP TS 25.832-v400: Manifestations of Handover and SRNS Relocation 3GPP TS 26.071-v400: AMR Speech Codec General Description WCDMA Radio Transmission and Resource Management 3GPP TS 25.101-v410: UE Radio Transmission and Reception FDD 3GPP TS 25.104-v410: BS Radio Transmission and Reception FDD 3GPP TS 25.133-v410: Requirements for Support of Radio Resource Management WCDMA Physical Layer Specifications FDD and TDD 3GPP TS 25.201-v400: Physical Layer General Description 3GPP TS 25.301-v410: Radio Interface Protocol Architecture 3GPP TS 25.302-v410: Services Provided by the Physical Layer WCDMA FDD TDD Mode Standards: 3GPP TS 25.211-v410: Physical channels and mapping of transport channels onto physical channels FDD 3GPP TS 25.212-v410: Multiplexing and channel coding FDD 3GPP TS 25.213-v410: Spreading and modulation FDD 3GPP TS 25.214-v410: Physical layer procedures FDD 3GPP TS 25.215-v410: Physical layer - Measurements FDD 3GPP TS 25.221-v400: Physical channels and mapping of transport channels onto physical channels TDD 3GPP TS 25.222-v410: Multiplexing and channel coding TDD 3GPP TS 25.223-v410: Spreading and modulation TDD 3GPP TS 25.224-v410: Physical layer procedures TDD 3GPP TS 25.225-v410: Physical layer - Measurements TDD This presentation is current as of TS-25 Rel-4 3GPP June 2001 Release Figure 4-2: Specifications Referenced in this Course. Many of the figures in the rest of this chapter contain a reference to the specification document and chapter from which the information was taken. These documents are checked and updated regularly. Both the Frequency and Time Division Duplex FDDTDD modes of operation are covered by the standardization documents. The TDD mode of operation allows a complete network to be deployed with only 5 MHz of frequency spectrum whereas FDD requires at least 10 MHz. Therefore the TDD mode is especially useful in countries where the IMT-2000 frequency spectrum has already been allocated to another system as is the case in the USA where PCS operators currently use the IMT-2000 spectrum. One solution is to use WCDMA TDD in the unlicensed PCS band between the uplink and downlink 1910 MHz to 1930 MHz. Unlike IS-95 and CDMA2000 WCDMA FDD base stations do not require GPS synchronization. This is important where the network requires indoor base stations as it may be difficult to site the GPS antenna.

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WCDMA Air Interface - 96 - EN/LZT 123 7279 R4A Another body known as the Operators Harmonization Group OHG works towards ensuring that WCDMA and CDMA2000 Radio Access Networks will be hardware compatible with ANSI-41 equipment. This will make it easier for operators to add WCDMA and CMDA2000 equipment to their existing GSM or GPRS networks. The physical layer for WCDMA supports data rates of 15 30 60 120 240 480 960 and 1920 ksymbols/s. Note that the 2048 kbps payload rate is achieved by using several physical layer channels or codes simultaneously. This is known as multi-code operation. 2025 2110 IMT-2000 MSS MSS IMT-2000 MSS MSS 1885 1980 2010 2160 2170 2200 ITU/ WARC-95 2025 2110 IMT-2000 MSS IMT-2000 MSS 1900 1980 2010 2170 2200 DECT 1880 Europe 2025 2110 IMT-2000 MSS Terrestrial MSS 1918.1 1980 2010 2170 2200 PHS 1895 1885 Japan 2025 2110 MSS MSS 1900 1980 2010 2170 2200 FDD WLL 1880 CDMA 1865 1920 1945 1960 TDD WLL CDMA FDD WLL China 2025 2110 MSS 2185 2200 A 1850 1910 1930 1990 D B E F C A D B E F C MSS Broadcast Auxiliary Reserved 2150 USA 2025 2110 FDD UPLINK TDD FDD DOWNLINK 1920 1980 2010 2170 WCDMA / EUROPE 1850 1910 FDD UPLINK 1930 1990 WCDMA / USA FDD DOWNLINK TDD TDD 1900 3GPP TS 25.201 ¶ 5.2 25.102 ¶ 5.2.2 3GPP TS 25.201 ¶ 5.2 25.102 ¶ 5.2.2 Figure 4-3: WCDMA Frequency Allocations. Figure 4-3 shows the frequency allocations used in various parts of the world. The figure shows that the IMT-2000 spectrum has already been allocated to PCS operators in the USA. The unlicensed PCS band 1910 MHz to 1930 MHz may be used with TDD mode to deploy WCDMA networks in this area. Other proposals recently forward for WCDMA spectrum in the USA as follows: • 2500 - 2690 MHz giving 190 MHz. Currently being used for fixed wireless services by Sprint and WorldCom. • 1710 - 1755 MHz giving 45 MHz. Currently being used for Government and commercial services. • 1755 - 1850 MHz giving 95 MHz. Currently being used by Defense Forces. • 2110 - 2150 MHz giving 40 MHz. Currently being used by fixed and mobile services.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 97 - • 2160 - 2165 MHz giving 5 MHz. Currently being used by fixed and mobile services. The MSS blocks have been allocated to Mobile Satellite Systems. It is hoped that these will be used to help achieve seamless global coverage. GSM/GPRS Core Network CN I u I u RNS RNC RNS RNC RBS RBS RBS RBS I ur I ub I ub I ub I ub User Equipment UE UTRAN WCDMA RAN UMTS Terrestrial Radio Access Network PSTN ISDN Internet U u MSC GPRS Service Node I u I u Figure 4-4: UMTS and the WCDMA RAN The main WCDMA RAN interfaces are Iu Iur and Iub Figure 4-4. Iu is the interface between WCDMA RAN and the core network. There are two types of interfaces in the Iu interface: the Iu interface towards the Packet-Switched PS network GPRS and the Iu interface towards the Circuit-Switched CS network MSC. The Iu interface supports several functions such as establishing maintaining and releasing radio access bearers RAB performing intra-system and inter-system handover location services by transferring requests from the Core Network CN to the WCDMA RAN and location information from the WCDMA RAN to the CN. Iur interfaces radio network controllers and is required to support inter RNC soft handover. The Iub is a logical interface that connects the RBS to the RNC. WCDMA RAN definitions: • RNS Radio Network Subsystem A full or partial network offering access between UE and the Core Network.

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WCDMA Air Interface - 98 - EN/LZT 123 7279 R4A • RNC Radio Network Controller Element of the RNS that controls physical radio resources. • RBS Logical node controlling transmission and reception from one or more cells. • U u interface Interface between UE and RBS. • I u interface Interface between the CN and the RNS. • I ur interface Interface between the RNS and another RNSs. • I ub interface Interface between the RNC and RBS. WCDMA RAN Operational Functions: Functions related to overall system access control: • Admission Control Congestion Control • System information broadcasting • Radio channel ciphering and deciphering. Functions related to mobility: • Handover • SRNS Relocation. Functions related to radio resource management and control: • Initial random access detection and handling • Radio resource configuration and operation

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 99 - • Combining/splitting control • Radio bearer connection set-up and release Radio Bearer Control • Allocation and de-allocation of Radio Bearers • Radio protocols function • RF power control • Radio channel coding • Radio channel decoding. WCDMA OSI MODEL The Radio Access Network is divided into a user plane and a control plane Figure 4-5. The user plane is used for sending user data while the control plane is used for signaling. L2 L1 L2 L3 WCDMA RAN UE RRC RLC MAC PHY RRC MAC PHY RLC RLC RLC Signaling Radio Bearer Radio Bearer Logical Channel Transport Channel Physical Channel CTRL CTRL USER DATA USER DATA Figure 4-5: WCDMA RAN OSI Model. In the WCDMA Open Systems Interconnection OSI model it can be seen how the three layers are connected using logical transport and physical channels. The Radio Resource Control RRC handles most of the signaling between the UE and the RNC. It is in direct control of the physical layer for call setup release etc.

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WCDMA Air Interface - 100 - EN/LZT 123 7279 R4A A Radio Access Bearer RAB is the connection segment between the UE and the Core Network to support Quality of Service QoS for UMTS bearer services. Each of the RABs is mapped onto one or more Radio Bearers. Each Radio Bearer is mapped onto one Radio Link Control RLC entity. Each RLC entity communicates UE-RNC with its peer entity using one or more logical channels. Logical channels are grouped by information content that is by whether they carry user data or L3 signaling. This L3 signaling is used to send information such as measurement reports and handover commands. These logical channels are mapped onto transport channels by the Medium Access Control MAC layer. The transport channels are grouped by the method of transport used dedicated or common. Finally the transport channels are mapped onto physical channels. The physical channels are distinguished by RF frequency channelization code scrambling code and modulation. In other words these channels perform the actual transmission of data bits. Services provided by the Physical Layer: • FEC Forward Error Correction encoding/decoding of transport channels • Error detection on transport channels and indication to higher layers • Rate matching of coded transport channels to physical channels. • Power weighting and combining of physical channels. • Inner-loop power control • Modulation/demodulation and spreading/de-spreading of physical channels • Multiplexing/de-multiplexing of coded composite transport channels • Macro diversity distribution/combining. Procedures: • Cell search functions • Synchronisation chip bit and frame synchronisation • Soft handover support

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 101 - • Radio characteristics measurements including FER Frame Erasure Ratio SIR Signal-to-Interference Ratio Interference Power and indication to higher layers Figure 4-6 shows a summary of the different physical channels used in both uplink and downlink. Detailed explanations of these channels are provided separately for the downlink and uplink channels. It should be noted that the Dedicated Physical Data Channel DPDCH contains user data and L3 signaling for example handover reports and commands. The Dedicated Physical Control Channel DPCCH contains only L1 control data for example power control messages.

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WCDMA Air Interface - 102 - EN/LZT 123 7279 R4A Radio Base Station RBS User Equipment UE P-CCPCH- Primary Common Control Physical Channel SCH - Synchronization Channel P-CPICH - Primary Common Pilot Channel Common physical channels DPDCH - Dedicated Physical Data Channel DPCCH - Dedicated Physical Control Channel Dedicated physical channels PICH - Page Indicator Channel S-CCPCH - Secondary Common Control Physical Channel PRACH - Physical Random Access Channel AICH - Acquisition Indicator Channel Figure 4-6: WCDMA Physical Channels in uplink and downlink WCDMA DOWNLINK A block diagram of a typical downlink WCDMA transmitter cell is shown in Figure 4-7.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 103 - WCDMA Downlink FDD BCCH Broadcast Control Ch. PCCH Paging Control Ch. CCCH Common Control Ch. DCCH Dedicated Control Ch. DTCH Dedicated Traffic Ch. N BCH Broadcast Ch. PCH Paging Ch. FACH Forward Access Ch. DCH Dedicated Ch. P-CCPCH Primary Common Control Physical Ch. S-CCPCH Secondary Common Contr ol Physical Ch. DPDCH one or more per UE Dedicated Physical Data Ch. DPCCH one per UE Dedicated Physical Control Ch. Pilot TPC TFCI bits SSC i Logical Channels Layers 3+ Transport Channels Layer 2 Physical Channels Layer 1 Downlink RF Out DPCH Dedicated Physical Channel One per UE DSCH Downlink Sh ared Ch. CTCH Common Traffic Ch. CPICH Common Pilot Channel Null Data Data Encoding Data Encoding Data Encoding Data Encoding Data Encoding PDSCH Physical Downlink Shared Channel AICH Acquisition Indicator Channel PICH Paging Indicator Channel Access Indication data Paging Indication bits AP-AICH Access Preamble Indicator Channel Access Preamble Indication bits CSICH CPCH Status Indicator Channel CPCH Status Indication bits CD/CA-ICH Collision Detection/Channel Assignment CPCH Status Indication bits S/P S/P C ch S/P S/P S/P S/P S/P S/P S/P S/P I+jQ I/Q Modulator Q I C ch C ch C ch C ch C ch C ch C ch C ch 2561 C ch 2560 Σ G S PSC G P Σ Sync Codes Note regarding P-CCPCH and SCH Sync Codes are transmitted only in bits 0-255 of each timeslot P-CCPCH transmits only during the remaining bits of each timeslot Σ Filter Filter Gain Gain Gain Gain Gain Gain Gain Gain Gain Gain SCH S ync Channel DTCH Dedicated Traffic Ch. 1 DCH Dedicated Ch. Data Encoding M U X M U X CCTrCH DCH Dedicated Ch. Data Encoding S dln S dln S dln S dln S dln S dln S dln S dln S dln S dln Figure 4-7: WCDMA Downlink FDD. This figure shows how the logical channels are mapped onto transport channels and further onto physical channels. The transport channels are going through data encoding CRC FEC Interleaving before they are mapped onto the physical channels. The downlink indication channels do not have transport channels mapped onto them as they only exist in the physical layer. The physical channels are passed through a serial to parallel S/P converter to create two separate data streams the I- and the Q- branch. These are then multiplied with the channelization code to achieve the 3.84 Mchips/s. The scrambling code is then applied for every channel. This is due to that an alternative code tree can be needed if compressed mode see dedicated physical channels is used for dedicated channels. In this case a secondary scrambling code is used. After this a power gain factor is applied on each physical channel and these are then summarized. The synchronization codes are added after the summation is performed. The reason for this is that they indicate which scrambling code used in the cell. Finally the signal is filtered modulated amplified and sent out in the air. Each channel will be described further in this chapter.

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WCDMA Air Interface - 104 - EN/LZT 123 7279 R4A LOGICAL CHANNELS Logical channel types are classified into two groups: • Control channels for the transfer of control information • Traffic channels for the transfer of user information. The Broadcast Control Channel BCCH is a downlink channel for broadcasting system information. Paging Control Channel PCCH is a downlink channel that transfers paging information and is used when the UE is in idle mode. The Common Control Channel CCCH is a bi-directional channel that transfers control information between the network and UE. This channel is used by the UE needs to access the network. The Dedicated Control Channel DCCH is a point-to-point bi-directional channel that transmits dedicated control information between UE and the network. This channel is established through a RRC connection setup procedure. The Dedicated Traffic Channel DTCH is a point-to-point channel dedicated to one UE for transferring user information. A DTCH can exist in the uplink and downlink. TRANSPORT CHANNELS A transport channel is defined by how and with what characteristics data is transferred over the air interface. There are two types of transport channels: • Common channels • Dedicated channels. There is one dedicated transport channel the Dedicated Channel DCH which is used in both downlink and uplink. The DCH is characterized by the possibility of fast rate change and fast power control. The Broadcast channel BCH is a downlink transport channel that is used to broadcast system and cell specific information. The BCH is always transmitted over the entire cell with a low fixed bit rate. The Forward Access Channel FACH is a downlink transport channel that carries control information to UEs when a random access message has been sent by the UE to the base station. The Paging Channel PCH is a downlink transport channel used for paging.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 105 - PHYSICAL CHANNELS A brief explanation of the function of the physical channels that are transmitted to all UEs are referred to as ‘common downlink physical channels’ follows. Common Downlink Physical Channels: • Primary Common Control Physical Channel P-CCPCH: Broadcasts system information. • Synchronization Channel SCH: Carries Primary and Secondary Synchronization Codes used for slot synchronization frame synchronization and the detection of the scrambling code group one out of 64. It is time multiplexed only first 10 with the P-CCPCH remaining 90 of timeslot. • Secondary Common Control Physical Channel S- CCPCH: Carries both the Paging Channel PCH and the Forward Access Channel FACH. Transmits idle-mode signaling and control information to UE. Can also be used for sending short infrequent data. • Primary Common Pilot Channel P-CPICH: Sends the scrambling code of the cell. Provides coherent phase reference for DL channels and aids channel estimation handover and cell selection. Downlink channels that are transmitted to particular UEs are called Dedicated Physical Channels. Dedicated Downlink Physical Channels: • Dedicated Downlink Physical Data Channel DPDCH: Used for sending dedicated data and L3 signalling. • Dedicated Downlink Physical Control Channel DPCCH: Transmits layer 1 signaling to UE including Transmit Power Control TPC bits pilot bits and Transport Format Combination Indicator TFCI bits.

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WCDMA Air Interface - 106 - EN/LZT 123 7279 R4A The list of channels below concentrates on the downlink physical channels that are used to indicate a particular situation to the UE. These channels can be referred to as ‘downlink indication channels’. These channels only exist in the physical layer that is they do not have any transport channels mapped onto them. Downlink Indication Channels: • Acquisition Indicator Channel AICH: Acknowledges that the RBS has acquired a UE Random Access attempt Echoes the UE’s Random Access signature. • Paging Indicator Channel PICH: Informs a UE to monitor the next paging frame. CHANNELIZATION CODE INDEX As explained earlier channelization codes vary in length depending on the input data rate. This gives rise to these codes being called Orthogonal Variable Spreading Factors OSVF. The codes are created from the Channelization Code Tree. Figure 4-8 shows the beginning of this tree. Each branch is sub-divided in two to create two new codes one is simply the code repeated and the other is the code followed by the inverse of the code. The Spreading Factor SF increases as the codes increase in length that is short codes produce a low spreading factor while longer codes produce a higher spreading factor. The various codes are denoted by “C SFcode number ” . 1 1 -1 1 1 1 1 1 1 1 1 -1 -1 1 -1 1 -1 1 -1 -1 1 C 10 C 20 C 21 C 40 C 41 C 42 C 43 SF 1 SF 2 SF 4 Figure 4-8: Channelization Code Index.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 107 - COMMON PILOT CHANNEL The Common Pilot Channel CPICH shown in Figure 4-9 provides a coherent phase reference for the downlink channels. The CPICH continuously sends the scrambling code for the cell. It also aids channel estimation for cell selection/reselection and handover for the UE. By adjusting the CPICH power level the cell size and load between different cells can be balanced. Pilot Symbol Data 10 symbols per slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 Frame 15 slots 10 mSec 1 timeslot 2560 Chips 10 symbols 20 bits 666.667 uSec 3GPP TS 25.211¶ 5.3.3 3GPP TS 25.211¶ 5.3.3 Figure 4-9: The Common Pilot Channel. WCDMA uses 18 shift registers to create the scrambling codes used in the downlink. This produces a code length of 262143 2 18 - 1 chips however only the first 38400 chips are used by the system. Since the chip rate is 3.84 Mchips/s it will take the system 10 ms 38400/3.84·10 6 to send 38400 chips. This time duration is referred to as one frame. The frame is sub-divided into 15 slots each containing 2560 38400/15 chips. The duration of one slot is 10·10 -3 /15 s i.e. 666.667 µs. Figure 4-9 shows how the Common Pilot Channel is mapped onto one of these timeslots. The length of the channelization code used for this channel C 2560 is 256 chips therefore ten modulation symbols or 10·2 20 bits of pilot information can be contained in one slot. PRIMARY COMMON CONTROL PHYSICAL CHANNEL AND SYNCHRONIZATION CHANNEL The Primary Common Control Physical Channel P-CCPCH is used to carry the broadcast channel BCH and the synchronization channel SCH. Figure 4-10 shows the structure of the Primary Common Control Physical Channel P-CCPCH which shows that the SCH and P-CCPCH are time multiplexed.

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WCDMA Air Interface - 108 - EN/LZT 123 7279 R4A This channel has a fixed rate of 30 kbps SF256. Common control physical channels are not inner-loop power controlled and are continuously transmitted over the entire cell. C 2561 is always used for this channel since it needs to be decoded by all UEs. Broadcast Data 18 bits SSC i BCH Spreading Factor 256 1 Slot 0.666 mSec 18 BCH data bits / slot 1 Frame 15 slots 10 mSec 2304 Chips 256 Chips SCH BCH 3GPP TS 25.211¶ 5.3.3.2 3GPP TS 25.211¶ 5.3.3.2 PSC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0 Figure 4-10: Synchronization Channel/Primary Common Control Channel. As with the pilot channel each slot contains 2560 chips however the first 256 chips are used to transmit the synchronization channel that contains a primary and a secondary synchronization code. This leaves 2560 - 256 2304 chips to carry the broadcast channel. Since the spreading factor is 256 each slot contains 2304/256 9 modulation symbols or 9·2 18 bits of broadcast information. SECONDARY COMMON CONTROL PHYSICAL CHANNEL The Secondary Common Control Physical Channel S-CCPCH Figure 4-11 is used to transmit two different transport channels: the forward access channel FACH and the paging channel PCH. Spreading Factor 256 to 4 1 Slot 0.666 mSec 2560 chips 20 2 k data bits k 0..6 1 Frame 15 slots 10 mSec 20 to 1256 bits 0 2 or 8 bits 3GPP TS 25.211¶ 5.3.3.2 3GPP TS 25.211¶ 5.3.3.2 Data TFCI or DTX Pilot 0 8 or 16 bits 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 109 - Figure 4-11: The Secondary Common Control Channel. This channel is mainly monitored by the UE in idle mode but can also be used in connected mode Cell_FACH. In Cell_FACH it is used to send low rate PS services as well as L3 signaling. As the type of transport channel transmitted using this physical channel varies Transport Format Combination Indication TFCI or Discontinuous Transmission DTX bits need to be sent to inform the receiving side of the channel types and bit rates. Zero eight or sixteen bits are used at the end of the frame as a pilot sequence for coherent detection. The data carried in this channel has a spreading factor of 256 to 4. PAGING INDICATOR CHANNEL Figure 4-12 below depicts the structure of the Paging Indicator Channel PICH. b 1 b 0 288 bits for paging indication 12 bits undefined One radio frame 10 ms b 287 b 288 b 299 Figure 4-12: The Paging Indicator Channel. This channel is used together with the Paging Channel PCH to provide UEs with an efficient sleep mode operation to save battery in idle mode. The PICH is used to alert UEs of an incoming page sent on the S-CCPCH. This is a Layer 1 channel only that is it originates in the physical layer.

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WCDMA Air Interface - 110 - EN/LZT 123 7279 R4A The PICH channel consists of 300 bits over one radio frame and uses a spreading factor of 256 which is given on the P-CCPCH. Only the first 288 of these bits are used to carry the Paging Indicators PIs which leaves the last 12 bits undefined. One PI requires 2–16 bits and so the number of PIs in one frame can vary from 18-144. The UEs are divided into paging groups and each paging group belongs to a specific PI. The UE calculates the PI using its IMSI number. The UE reads how often it should listen to the PI on the P-CCPCH. This time period is defined as the Discontinuous Reception DRX cycle. If the PI is set to 1 there is an incoming paging message and the UEs belonging to that PI wakes up and monitors the PCH message carried on the S-CCPCH. The IMSI is used to identify which UE that is paged. The rest of the UEs in the paging group will go back to idle mode. If the PI is set to 0 the UE remains in sleep mode. DEDICATED PHYSICAL CONTROL AND DATA CHANNEL Figure 4-13 below shows how the dedicated physical data channel DPDCH and the dedicated physical control channel DPCCH are time multiplexed onto one WCDMA slot in the downlink. Data 2 TFC I Data 1 TPC 1 Slot 0.666 m Sec 2560 chips 10 x 2k bits k 0... 7 SF 512/2 k 512 256 128 64 32 16 8 4 1 Fram e 15 slots 10 m Sec DPD CH Pilot DPD CH DP C CH DP CCH The DPDCH carries user traffic layer 2 overhead bits and layer 3 signaling data. The DPCCH carries layer 1 control bits: Pilot TPC and TFCI Downlink C losed -Loop Power Control steps of 1 dB 0.5 dB The DPDCH carries user traffic layer 2 overhead bits and layer 3 signaling data. The DPCCH carries layer 1 control bits: Pilot TPC and TFCI Downlink C losed -Loop Pow er Control steps of 1 dB 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0 Figure 4-13: The DPDCH and DPCCH. The DPDCH carries user traffic and Layer 3 signaling. The DPCCH carries Layer 1 control bits which are as follows:

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 111 - • Pilot bits which are used by the receiver to make different types of measurements. • Transmit Power Control TPC bits which are used in the inner loop power control. • Transport Format Combination Indicator TFCI bits which are used to inform the receiver about the transport format used. The SF varies from 512 to 4 to allow it to carry variable data rates. Bits/Frame Bits/ Slot DPCCH Channel Bit Rate kbps Channel Symbol Rate ksps SF TOTAL DPDCH DPCCH TOTAL DPDCH TFCI TPC PILOT 15 7.5 512 150 60 90 10 40 2 4 120 60 64 1200 900 300 80 60 8 4 8 1920 960 4 19200 18720 480 1280 1248 8 8 16 Coded Data 1.920 Mb/sec 19200 bits per 10 mSec frame S/P Converter Channel Coding OVSF codes at 3.84 Mcps 960 kb/sec Figure 4-14: Downlink Data Rates. Figure 4-14 shows how various user data rates are carried by the DPDCH and the DPCCH. Note that the symbol rate is always half the channel bit rate because of the serial to parallel conversion. If the required data rate is 15 kbps then after serial to parallel conversion the data is carried at a rate of 15/2 7.5 kbps by two separate streams. These streams are multiplied by a channelization code with a spreading factor of 512. Since 512 chips are used to transfer one modulation symbol 38400/512 75 modulation symbols or 75·2 150 bits will be carried in one frame. 60 of these are used to carry data in the DPDCH and 90 to carry L1 control information in the DPCCH. Since there are 15 slots in a frame the number of bits per slot will be 10. The DPDCH contains 4 of those bits and the remaining 6 bits are used by the DPCCH. Figure 4-15 provides an extract from the slot format table which shows the specified downlink DPDCH and DPCCH slot formats.

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WCDMA Air Interface - 112 - EN/LZT 123 7279 R4A 14 480 240 16 320 56 232 8 8 16 15 14A 480 240 16 320 56 224 8 16 16 8-14 14B 960 480 8 640 112 464 16 16 32 8-14 15 960 480 8 640 120 488 8 8 16 15 15A 960 480 8 640 120 480 8 16 16 8-14 15B 1920 960 4 1280 240 976 16 16 32 8-14 16 1920 960 4 1280 248 1000 8 8 16 15 16A 1920 960 4 1280 248 992 8 16 16 8-14 DPDCH Bits/Slot DPCCH Bits/Slot Slot Format i Channel Bit Rate kbps Channel Symbol Rate ksps SF Bits/ Slot N Data1 N Data2 N TPC N TFCI N Pilot Transmitted slots per radio frame N Tr 015 7.5 51210 0 4 2 0 4 15 0A 15 7.5 512 10 0 4 2 0 4 8-14 0B 30 15 256 20 0 8 4 0 8 8-14 115 7.5 51210 0 2 2 2 4 15 1B 30 15 256 20 0 4 4 4 8 8-14 2 30 15 256 20 2 14 2 0 2 15 2A 30 15 256 20 2 14 2 0 2 8-14 2B 60 30 128 40 4 28 4 0 4 8-14 3 30 15 256 20 2 12 2 2 2 15 3A 30 15 256 20 2 10 2 4 2 8-14 3B 60 30 128 40 4 24 4 4 4 8-14 Figure 4-15: Downlink DPDCH/DPCCH Slot Formats. Two points to note are: • Slot formats with no TFCI bits are used only when there is one data service in the DCH • Slot formats ending with A or B are used for compressed mode operation. As can be seen from the table only 8 to 14 slots are transmitted in each frame thereby giving time for the UE to measure the signal levels from non-WCDMA networks GSM or to make hard handovers to WCDMA carriers on other frequencies. Figure 4-16 shows how compressed mode can be used to create transmission gaps.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 113 - 3GPP TS 25.212 ¶ 4.4.3 3GPP TS 25.212 ¶ 4.4.3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 2 3 4 5 11 12 13 14 15 6 1 2 3 4 5 11 12 13 14 15 1 2 3 4 5 11 12 13 14 15 6 1 2 3 4 5 6 7 8 9 10 11 12 4 5 11 12 13 14 15 6 10 mSec Frames 15 slots Normal Operation Compressed-Mode single-frame method Compressed-Mode double-frame method Transmission Gap Transmission Gap The complete TFCI word must be transmitted every frame even in Compressed Mode. Compressed Mode Slot formats AB contain higher proportion of TFCI bits per slot compared with normal slots. Figure 4-16: Compressed mode Figure 4-17 shows how the pilot symbols are embedded in the different slots in one frame. Npilot 4 Npilot 8 Npilot 16 Symbol 0 1 0 1 2 3 0 1 2 3 4 5 6 7 Slot 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 00 01 00 10 11 11 10 01 11 01 10 10 00 00 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 00 01 00 10 11 11 10 01 11 01 10 10 00 00 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 10 10 01 00 01 10 00 00 10 11 01 11 00 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 00 01 00 10 11 11 10 01 11 01 10 10 00 00 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 10 10 01 00 01 10 00 00 10 11 01 11 00 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 10 01 11 01 10 10 00 00 11 00 01 00 10 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 10 00 00 10 11 01 11 00 11 11 10 10 01 00 01 Pilot Bit Patterns Downlink DPDCH Data Channel Figure 4-17: Time-Embedded Pilot Symbols. The pilot bits are used for SIR measurements used in the inner loop power control. The grey fields are called Frame Synchronization Words FSW and are used for synchronization measurements. Figure 4-18 shows how the different TPC bit formats are used to request power increases or decreases.

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WCDMA Air Interface - 114 - EN/LZT 123 7279 R4A TPC Command N TPC 2 N TPC 4 N TPC 8 Up 1 11 1111 11111111 Down 0 00 0000 00000000 Figure 4-18: Transmit Power Control TPC Bits. Since power control is very important and no form of error protection is used on these bits the bits are sent more than once to achieve some level of error protection. At low data rates where the SF is high the TPC bit is only sent twice. In the case of high data rate channels where the SF is much smaller up to eight TPC bits are sent. Figure 4-19 below explains in more detail how the Transport Format Combination Indicator TFCI bits are generated. As this information is vital for decoding each frame strong error protection is used thereby increasing these 10 bits to 32 bits. Data Channel 1 Data Channel 2 Data Channel N Channel Coding Channel Coding Channel Coding Coded Composite Transport Channel CCTrCH TFI 1 TFI 2 TFI N MUX MUX TFCI Word 32 bits TFI: Transport Format Indicator TFCI: Transport Format Combination Indicator Channel Coding 10 bits Figure 4-19: TFCI Bits. It is vital that the whole 32-bit TFCI word is sent in each frame. This is achieved in compressed mode by sending more TFCI bits per timeslot. In slot format 3A for example four bits are sent per slot. If only eight slots are sent per frame this means that the complete word 8·4 32 will still be transmitted in each frame. In normal mode operation only 30 bits are transferred 15·2 and two bits are therefore punctured. As this word is strongly coded these two bits will be treated like errors and corrected.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 115 - Acquisition Indicator Channel The acquisition indicator channel AICH is a physical channel used to carry acquisition indicators which corresponds to a certain signature that the UE selected randomly on the PRACH. AICH is a fixed rate SF256 channel. It uses 15 consecutive access slots corresponds to 2 slots each of length 5120 chips. Each access slot consists of two parts. The first part is the Acquisition Indicator AI consisting of 32 symbols. The second part consists of 1024 chips and here the transmission is off. The AI part takes the values +1 -1 and 0. The b sj is the signature pattern. Figure 4-20 shows the structure of the AICH as specified by the 3GPP. The AI part is derived from the UEs access preamble signature. 1024 chips AS 0 AS 1 AS i AS 14 a 1 a 2 a 0 a 31 a 30 AI part 20 ms AS 14 AS 0 Transmission Off ∑ 15 0 s j s s j b AI a Figure 4-20: Acquisition Indication Channel AICH. MULTIPLEXING Figure 4-21 shows the Ericsson mapping of a 12.2 kbps speech RAB L3 signaling together with L1 signaling onto a DPCH.

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WCDMA Air Interface - 116 - EN/LZT 123 7279 R4A 119 119 119 119 2 nd speech block 152 167 68 600 600 600 600 2 110 1 110 152 167 68 476 8 tail bits CRC 16 164 148 516 Rate 1/3 CC 1st interleaving MAC Layer 4 bit MAC 136 RRC UM 8 bit RLC RRC AM or NAS DT normal priority 128 128 144 16 bit RLC 4 bit MAC 40 msec Frame segmentation 136 2 nd interleaving 510 119 2 nd interleaving 510 119 1st interleaving 144 DPDCH 60ksps SF128 DPDCH 60kbps SF128 2 TPC 4 Pilot 2 TPC 4 Pilot Convolutional coding 8 tail bits CRC 12 93 303 1/3 333 1/3 136 1/2 81 103 60 103 60 81 Rate matching 20 msec of each subflow 34 34 34 34 40 40 40 40 316 294 172 294 316 172 147 147 158 158 86 86 147 158 86 147 158 86 Figure 4-21: Downlink speech RAB mapping. Since speech can only cope with a short interleaving delay 20 ms blocks of speech data are used. With a data rate of 12.2 kbps this corresponds to 244 bits. This block is divided into 3 sub flows indicating the significance of the bits from the vocoder. The L3 signaling uses 40 ms blocks and passes through similar steps as the voice. 12 bits of CRC is added to voice and 16 to L3 signaling. To reset the convolutional coder 8 tail bits must be added. The resulting bits are fed to the convolutional coder. Sub flow 1 and 2 and the L3 signaling uses 1/3 convolutional coding and sub flow 3 uses 1/2 convolutional coding. The next step is rate matching that reduces the amount of bits by puncturing to match the DPCH bit rate. The first stage of interleaving is service dependent and will in this case be 20 ms for voice and 40 ms for the L3 signaling. To have the same time period of data two 20 ms voice blocks must be taken for each L3 signaling block. The voice and L3 signaling are multiplexed onto four 10 ms radio frames. The second interleaving length is always 10 ms long. The frame is then divided into 15 slots and finally the L1 signaling bits are multiplexed. In this case the final symbol rate after serial to parallel conversion will be 30 ksps and a SF of 128 is used. Figure 4-22 shows the Ericsson mapping of a 384 kbps PS RAB L3 signaling together with L1 signaling onto a DPCH.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 117 - 95 95 95 95 Next 3 blocks 380 8 tail bits CRC 16 164 148 516 Rate 1/3 CC 1st interleaving MAC Layer 4 bit MAC 136 8 bit RLC 128 128 144 16 bit RLC 4 bit MAC 40 msec 136 144 12 Trellis termination bits 9025 95 2 nd interleaving 9120 608 608 DPDCH 480ksps SF8 9025 Turbo Coding 12672 16 16 16 16 16 16 16 16 16 16 16 16 320 320 320 320 16 16 16 16 320 320 320 320 16 16 16 16 320 320 320 320 16 16 16 16 Up to 12X320 TBs in 10 msec max data rate 384 kbps Rate matching 1st interleaving 8 TFCI 8 TPC 16 Pilot 600 600 600 RRC UM RRC AM or NAS DT normal priority Figure 4-22: Downlink 384 kbps PS RAB mapping. Note that turbo coding is used for the PS data and that 10 ms is used for the first interleaving. Figure 4-23 shows how several downlink DPDCHs can be used for multi coding to achieve 2Mbps. Only one DPCCH is needed. Note that Ericsson is not supporting this. 1 Slot 0.666 mSec 2560 chips 10 x 2k bits k 0...7 Data 2 TFCI Data 1 TPC Pilot Primary DPCCH/DPDCH Data 4 Data 3 Additional DPCCH/DPDCH Data N Data N-1 Additional DPCCH/DPDCH Figure 4-23: Multi-Code Transmission. Transmit Diversity Different types of transmit diversity can be used at the base station to improve the capacity. Note that Ericsson is not supporting any of these today. These are Time-Switched Transmit Diversity TSTD and Space- Time Transmit Diversity STTD. TSTD is used only on the synchronization channels. These channels are alternated between antenna 1 and 2 for each slot in the WCDMA frame as shown in Figure 4-24.

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WCDMA Air Interface - 118 - EN/LZT 123 7279 R4A STTD is used on all other channels. The data bits are transmitted again on the second antenna with the phase reversed for each alternative bit. b 0 b 1 b 2 b 3 b 0 b 1 b 2 b 3 -b 2 b 3 b 0 -b 1 Antenna 1 Antenna 2 Data bits PSC SSCi PSC SSCi PSC SSCi PSC SSCi PSC SSCi Antenna 1 Antenna 2 Slot 0 Slot 1 Slot 2 Slot 3 Slot 14 • STTD Space-Time Transmit Diversity All Other DL Channels Note: TSTD and STTD must be supported by the UE but are optional in BS • TSTD Time-Switched Transmit Diversity SCH Only 3GPP TS 25.211 ¶ 5.3 3GPP TS 25.211 ¶ 5.3 Figure 4-24: RBS Transmit Diversity. The general transmitter structure of closed-loop diversity for DPCH signals is shown in Figure 4-25. This signal is fed to both antennas and weighted with antenna specific weight factors w 1 and w 2. These factors are complex valued w i a i + jb j . The UE measures the signal strength from the two antennas and computes the phase and amplitude adjustment that should be applied at the WCDMA RAN to maximize the UE received power. The UE transmits Feedback Information FBI bits that informs the RBS how to adjust the amplitude and phase relations between the two antennas.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 119 - Σ DPCCH DPDCH MUX DCH or PDSCH W 1 W 2 Σ CPICH 2 CPICH 1 Decode FBI Calculate Gains Phases Antenna 1 Antenna 2 Weights W1 W2 are complex-valued: W i a i + jb i gain i square root a i 2 + b i 2 phase i tan -1 b i /a i • S/P Demux • Channelization • Scrambling • I/Q Modulation Figure 4-25: Closed-Loop Transmit Diversity. When Site Selection Transmit Diversity is used the UE again uses the FBI bits in the DPCCH channel to report to the RBS. However this time these are used to indicate which antenna in a soft/softer handover scenario that is providing the best signal. The transmission of data on the DPDCH in the downlink of the various cells is then controlled by the indication bits. WCDMA UPLINK Figure 4-26 shows the structure of the WCDMA uplink UE as transmitter. The main difference between uplink and downlink is that the DPCCH and DPDCH are not time multiplexed. One reason for this is to improve the peak-to-average ratio.

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WCDMA Air Interface - 120 - EN/LZT 123 7279 R4A Logical Channels Layers 3+ Transport Channels Layer 2 Physical Channels Layer 1 Uplink RF Out UE Scrambling Code I+jQ I/Q Mod. Q I Ch c Σ Σ I Filter Filter CCCH Common Control Ch. DTCH packet mode Dedicated Traffic Ch. RACH Random Access Ch. PRACH Physical Random Access Ch. DPDCH 1 Dedicated Physical Data Ch. CPCH Common Packet Ch. PCPCH Physical Common Packet Ch. Data Coding Data Coding DPDCH 3 optional Dedicated Physical Data Ch. DPDCH 5 optional Dedicated Physical Data Ch. DPDCH 2 optional Dedicated Physical Data Ch. DPDCH 4 optional Dedicated Physical Data Ch. DPDCH 6 optional Dedicated Physical Data Ch. Σ Q DPCCH Dedicated Physical Control Ch. Pilot TPC TFCI bits Ch d G c G d j Ch d1 G d Ch d3 G d Ch d5 G d Ch d2 G d Ch d4 G d Ch d6 G d Ch c G d Ch c Σ Ch d G c G d j RACH Control Part PCPCH Control Part Σ j Σ DCCH Dedicated Control Ch. DTCH Dedicated Traffic Ch. N DCH Dedicated Ch. Data Encoding DTCH Dedicated Traffic Ch. 1 DCH Dedicated Ch. Data Encoding M U X CCTrCH DCH Dedicated Ch. Data Encoding Figure 4-26: WCDMA Uplink. The list below provides a brief explanation of the function of the Ericsson supported channels from the system side that are transmitted in the uplink. • Physical Random Access Channel PRACH: This channel is used to carry access requests control information and short data bursts. It uses only Open-loop power control and contains therefore no pilot or TPC bits. • Dedicated Physical Data Channel DPDCH: The uplink DPDCH is used to carry dedicated traffic and L3 signaling. • Dedicated Physical Control Channel DPCCH: The uplink DPCCH is used to carry layer 1 signaling. This information consists of pilot bits Transmit Power Control TPC commands Feedback Information FBI and Transport Format Combination Indicator TFCI. DEDICATED PHYSICAL CONTROL AND DATA CHANNEL Figure 4-27 shows the structure of the uplink DPDCH and DPCCH.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 121 - Coded Data 10 x 2k bits k0…6 10 to 640 bits Dedicated Physical Data Channel DPDCH Slot 0.666 mSec Pilot FBI TPC Dedicated Physical Control Channel DPCCH Slot 0.666 mSec 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 Frame 15 slots 10 mSec I Q TFCI Figure 4-27: Uplink DPDCH/DPCCH. The DPDCH and DPCCH are not time multiplexed. DPDCH uses the I-branch and the DPCCH uses the Q-branch. The spreading factor for the DPDCH can range from 4 to 256. The SF for the DPCCH is set to 256. The DPCCH consists of the following: • Pilot field uses 3 4 5 6 7 or 8 bits. • TFCI that is the Transmit Format Combination Indicator relating to how the data is multiplexed etc. uses 0 none 2 3 or 4 bits. • FBI that is the Feedback Information is used for transmit diversity. Here 0 none 1 or 2 bits can be used. • TPC that is Transmit Power Control used in inner loop power control uses 1 or 2 bits. Figure 4-28 shows different slot formats available for both the DPDCH and DPCCH. Seven different formats are available for the DPDCH ranging from slot format 0 which offers 15 kbps using a SF of 256 to slot format 6 which offers 960 kbps using a SF of 4. Twelve different slot formats are available for the DPCCH depending on the number of pilot TPC TPCI and FBI bits needed. Note that the formats ending in the letters A or B are special formats required in compressed mode operation to allow time for interfrequency measurements.

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WCDMA Air Interface - 122 - EN/LZT 123 7279 R4A Slot Format i C hanne l B it R ate kbps C hanne l Symbol R ate ksps SF Bits/ Frame Bits/ Slot N data 0 15 15 256 150 10 10 1 30 30 128 300 20 20 2 60 60 64 600 40 40 3 120 120 32 1200 80 80 4 240 240 16 2400 160 160 5 480 480 8 4800 320 320 6 960 960 4 9600 640 640 Slot Form at i Channe l Bit R ate kbps C hanne l Symbol R ate ksps SF Bits/ Frame Bits/ Slot N pilot N TP C N TFC I N FBI Transmitted slots pe r radio frame 0 15 15 256 150 10 6 2 2 0 15 0A 15 15 256 150 10 5 2 3 0 10-14 0B 15 15 256 150 10 4 2 4 0 8-9 1 15 15 256 150 10 8 2 0 0 8-15 2 15 15 256 150 10 5 2 2 1 15 2A 15 15 256 150 10 4 2 3 1 10-14 2B 15 15 256 150 10 3 2 4 1 8-9 3 15 15 256 150 10 7 2 0 1 8-15 4 15 15 256 150 10 6 2 0 2 8-15 5 15 15 256 150 10 5 1 2 2 15 5A 15 15 256 150 10 4 1 3 2 10-14 5B 15 15 256 150 10 3 1 4 2 8-9 DPDCH Dedicated Physical Data Channel Slot Formats DPCCH Dedicated Physical Control Channel Slot Formats Figure 4-28: Uplink DPDCH/DPCCH Slot Formats. Figure 4-29 shows the FBI bits. The overall field is made up of 0 1 or 2 bits depending on the slot format used. These are sub-divided into S and D fields. During soft handover the bits in the S field are used to inform the network which cell that is producing the strongest signal. This cell can be called the “primary cell” and the network can suspend transmission from other cells involved in the handover to reduce downlink interference. This enhancement to the soft handover process is called Site Selection Transmit Diversity SSTD. 3GPP TS 25.211 ¶ 5.2.1 3GPP TS 25.211 ¶ 5.2.1 S Field 0 1 or 2 bits Used for SSTD signaling during soft handover D Field 0 or 1 bit Provides feedback information for closed-loop transmit diversity 0 1 or 2 bits total depending on Slot Format SSTD Site Selection Transmit Diversity is an enhanced soft handover process The UE determines the cell with the strongest received signal and indicates this “primary cell” selection using the S Field. Cells other than the primary cell suspend transmission so that overall downlink interference is reduced. Figure 4-29: Feedback Information Field FBI. The D field bits are used in the Closed-loop transmit diversity loop which is used to control the gain and relative phase of the RBS transmit antennas in reaction to the received levels at the UE.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 123 - RANDOM ACCESS CHANNEL The random access message which is sent by the UE after it has received the acquisition on the AICH is shown in Figure 4-30. 3GPP TS 25.211¶ 5.2.2 3GPP TS 25.211¶ 5.2.2 Random Access Message 10 20 40 or 80 bits per slot RACH Data Slot 0.666 mSec Pilot 8 bits RACH Message Slot 0.666 mSec 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 Frame 15 slots 10 mSec I Q TFCI 2 bits Figure 4-30: Random Access Message. The RACH message can be configured to be 10 or 20 ms long. Ericsson has chosen 20 ms. The RACH message is sent on the I- branch while the layer 1 signaling is sent on the Q-branch. The control part uses SF 256 and consists of eight known pilot bits to support channel estimation for coherent detection and two TFCI bits. The RACH message uses SF 64. MULTIPLEXING Figure 4-31 shows the mapping of a 12.2 kbps speech RAB and L3 signaling on the DPDCH. The L1 signaling is sent on the DPCCH.

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WCDMA Air Interface - 124 - EN/LZT 123 7279 R4A Rate match 1 st Interleaving I Branch Q 140 140 140 140 2 nd speech block 152 167 68 600 b its 600 symbo ls 600 bits 600 sy m bols 600 600 40 40 2 110 40 40 1 110 152 167 68 129 129 129 129 8 tail bits CRC 16 164 148 516 Rate 1/3 CC 1st interleaving MAC Layer 4 bit MAC 136 8 bit RLC 128 128 144 16 bit RLC 4 bit MAC 40 msec Convolutional coding 8 tail bits Radio frame equalization 136 144 CRC 12 93 1/3 1/3 1/2 304 81 103 60 20 msec of each subflow 103 60 334 136 152 167 68 152 167 68 303+1 333+1 136 81 152 167 68 DPDCH 60kbps SF64 2 nd interleaving 600 40 40 140 Rate match 460 Q PILOT TFCI TPC 6 2 2 DPCCH 15kbps 152 167 68 DPDCH 60kbps SF64 2 nd interleaving 600 40 40 140 Rate match 360 Frame segmentation RRC UM RRC AM or NAS DT normal priority Figure 4-31: Uplink speech RAB mapping. The main difference between this procedure for the uplink and downlink is that for the uplink rate matching is performed after frame segmentation. Figure 4-32 shows the mapping of PS 64kbps RAB and L3 signaling on the DPDCH. The L1 signaling is sent on the DPCCH. I Branch Q 154 154 154 154 2 nd speech block 152 167 68 600 b its 600 sym b o ls 600 b its 600 sym bo ls 600 600 40 40 2 110 40 40 1 110 152 167 68 129 129 129 129 8 tail bits CRC 16 164 148 516 Rate 1/3 CC 1st interleaving MAC Layer 4 bit MAC 136 8 bit RLC 128 128 144 16 bit RLC 4 bit MAC 40 msec Frame segmentation 136 DPDCH 240kbps SF16 2 nd interleaving 2400 160 160 154 2246 Q PILOT TFCI TPC 6 2 2 DPCCH 15kbps DPDCH 240kbps SF16 2 nd interleaving 2400 160 160 154 2246 Rate matching 12 Trellis termination bits Up to 4X320 TBs in 20 msec max data rate 64 kbps 144 1st Interleaving 4236 Turbo Coding 4224 2118 2118 2246 2246 1 2 3 4 320 320 320 320 16 16 16 16 16 16 16 16 336 336 336 336 16 bit RLC CRC 16 RRC UM RRC AM or NAS DT normal priority Figure 4-32: Uplink PS 64 kbps RAB mapping.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 125 - HPSK MODULATION The top left-hand corner of Figure 4-33 below shows a vector diagram for the transmitter where the I- and Q-branches are of equal magnitude. Only the points are plotted. This represents the case in the downlink as the DPDCH and DPCCH are time multiplexed before being divided and sent to the I- and Q-branch. After baseband filtering shown in the top right hand diagram this traces the tip of the vector while the transmitter is in operation there are a lot of zero crossings. This means that the power out put of the transmitter represented by the length of the vector varies a lot between zero and full power. This result in a very poor peak-to- average transmit power ratio. QPSK IQ Equal Magnitude QPSK IQ Non-Equal Magnitude After Baseband Filtering Before Baseband Filtering After Baseband Filtering Before Baseband Filtering Figure 4-33: QPSK Modulation Pattern. The situation is even worse in the second case where I and Q are of non-equal magnitude as in the bottom left hand diagram in Figure 4-33. This will be the case in the uplink since the DPDCH is fed to the I-branch and the DPCCH is fed to the Q-branch. Due to discontinuous transmission of the DPDCH it results in more zero crossings. One method Figure 4-34 of reducing this is to use a type of modulation known as Complex Spreading. This works by using a complex scrambling code that rotates the whole pattern ±45 o or ±135 o to align with the I- and Q-branch. This is the type of modulation used in the downlink and the uplink when the data is multiplied by the complex scrambling code.

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WCDMA Air Interface - 126 - EN/LZT 123 7279 R4A Complex PN Spreading IQ Equal Magnitude Complex PN Spreading IQ Non-Equal Magnitude After Baseband Filtering Before Baseband Filtering After Baseband Filtering Before Baseband Filtering Figure 4-34: Complex Spreading Pattern. As can be seen from Figure 4-34 Complex Spreading rotates the transmitter vectors resulting in a more circular pattern even when I and Q are unequal in magnitude. This produces a lower peak to average ratio in the transmitter output and hence better transmitter efficiency and increased battery life. Hybrid Phase Shift Keying HPSK modulation is used in the uplink. As can be seen from Figure 4-35 restrictions are placed on the channelization codes that can be used in the uplink to avoid using those codes that have frequent positive and negative transitions. This reduces the number of zero crossings in the output and hence improves the peak-to-average power ratio of the RF transmitter. For the best possible transmitter efficiency and hence longest battery life this ratio must be kept to a minimum.

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4 WCDMA Physical Layer EN/LZT 123 7279 R4A - 127 - 1 1 -1 1 1 1 1 1 1 1 1 -1 -1 1 -1 1 -1 1 -1 -1 1 C 10 C 20 C 21 C 40 C 41 C 42 C 43 DPCCH DPDCH 1 2 DPDCH 3 4 DPDCH 5 6 Figure 4-35: Uplink Channelization Codes for HPSK. Code C 40 is used to spread the information from the DPCCH as this has the least zero transitions. After this C 41 is the first choice for a DPDCH of SF 4 as this produces only one zero transition. If more DPDCHs are required multi coding with the same SF then DPDCH_2 can use C 41 again I and Q branches are orthogonal to each other but this will be placed onto the Q branch of the modulator. The next DPDCH must use C 43 on the I-branch and so on. Code selection in this manner along with the proper choice of scrambling code increases the spectral efficiency by limiting the diagonal transmissions in the signal constellation. This also results in efficient use of the power amplifier. Also HPSK spreading uses Walsh rotator codes. When two consecutive pairs of I and Q chips have the same values i.e. 11 followed by 11 the transmitter output vector actually has to go from 11 down to zero and then back up to 11 again. This means that the output power has to vary a lot in a short time which is inefficient. The Walsh rotator codes multiply consecutive pairs of chips by 11 and 1 -1 so a 11 11 sequence becomes 11 1 -1 which is an easy 90 degree swing of the transmitter vector at constant amplitude constant power and is much more efficient.

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WCDMA Air Interface - 128 - EN/LZT 123 7279 R4A Complex PN Spreading IQ Equal Magnitude HPSK Spreading IQ Non-Equal Magnitude Complex PN Complex PN HPSK HPSK Figure 4-36: Complex PN Spreading vs. HPSKSpreading. The vector diagrams in Figure 4-36 compare the constellations produced when using complex scrambling and HPSK when I and Q are equal in the downlink and when I and Q are unequal in the uplink. Note that HPSK spreading is not actually used in the downlink it is merely shown here in the top right hand diagram for comparison. It can be seen that the HPSK constellation has a reduced incidence of zero crossings and hence an improved peak-to- average power ratio.

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5 WCDMA procedures EN/LZT 123 7279 R4A - 129 - 5 WCDMA procedures Objectives Upon completion of this chapter the student will be able to: • Explain base station downlink timing • Explain the synchronization procedure • Explain the random access procedure • Explain the establishment of dedicated channels • Explain soft handover timing

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WCDMA Air Interface - 130 - EN/LZT 123 7279 R4A Contents BASE STATION DOWNLINK TIMING ............................................... 131 SYNCHRONIZATION PROCEDURE ................................................. 131 DOWNLINK SCRAMBLING CODES ............................................................131 SYNCHRONIZATION CODES......................................................................132 RANDOM ACCESS PROCEDURE.................................................... 136 DEDICATED CHANNEL PROCEDURE............................................. 141 WCDMA SOFT HANDOVER.............................................................. 142

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5 WCDMA procedures EN/LZT 123 7279 R4A - 131 - BASE STATION DOWNLINK TIMING Figure 5-1 shows the transmission timing of the various downlink channels. The 256 chip gap in the beginning of each of the P- CCPCH slots is to accommodate the transmission of the SCH. The SCH is always transmitted from the base station and is transmitted at the same timing reference as the CPICH. The S-CCPCH is only transmitted when there is data available. Therefore it has its own transmission timing. This timing offset is a multiple of 256 chips. The variable time offset for downlink dedicated channels is to enable soft handover in an unsynchronized radio access network. The PICH has a fixed time offset with respect to the S-CCPCH to be able to alert the terminal that there is a page coming on the PCH mapped onto the S-CCPCH. Secondary SCH Primary SCH τ S-CCPCHk 10 ms Frame P-CCPCH SFN modulo 2 0 P-CCPCH SFN modulo 2 1 CPICH Common Pilot Channel AICH access slots 0 1 2 3 14 13 12 11 10 9 8 7 6 5 4 Any PDSCH τ PICH τ DPCHn Common Pilot Channel Primary CCPCH Broadcast Data Secondary CCPCH Paging Signaling Paging Indicator Channel SCH PSC+SSC P-CCPCH S-CCPCH PICH AICH PDSCH DPCH τ S-CCPCHk N x 256 chips τ DPCHn N x 256 chips τ PICH 7680 chips 3 slots 3GPP TS 25.211 ¶ 7.0 3GPP TS 25.211 ¶ 7.0 k:th S-CCPCH PICH for n:th S-CCPCH n:th DPCCH/DCDPH Downlink Shared Channel Dedicated Physical Control/Data Channel Figure 5-1: Downlink Transmission Timing. SYNCHRONIZATION PROCEDURE DOWNLINK SCRAMBLING CODES There are 8192 downlink scrambling codes available in total including secondary scrambling codes. The primary scrambling codes are 512 and these are divided into 64 different scrambling code groups. Each scrambling code group is further divided into eight codes. The grouping is done to facilitate fast cell search by the UE. This structure is shown in Figure 5-2.

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WCDMA Air Interface - 132 - EN/LZT 123 7279 R4A Prim ary SC 0 S eco n d ary Sc ra m b lin g Co d e s 15 Se c o n d a ry Sc ra m b lin g Co d e s 15 Se c o n d a ry Sc ra m b lin g Co d e s 15 S eco n d ary Sc ra m b lin g Co d e s 15 C ode G rou p 1 C ode G roup 64 8192 D ow n link Scram bling C odes E a ch code is 38 40 0 ch ips of a 2 18 - 1 26 21 43 ch ip G old S equ en ce Prim ary SC 7 Prim ary SC 50 4 Prim ary S C 51 1 Figure 5-2: DL scrambling codes. Each cell is assigned one primary scrambling code that is transmitted on the CPICH. SYNCHRONIZATION CODES The first 256 chips of each slot Figure 5-3 are reserved for transmission of the primary synchronization code PSC and secondary synchronization codes SSC. These codes are not scrambled with the primary scrambling code of the cell. The reason for this is that all UEs use these codes firstly to locate a WCDMA system and secondly to locate the scrambling code used in that cell. These 256 chip codes are broadcast every slot multiplexed with the P-CCPCH 2304 chips which allows the UEs to quickly synchronize to the network. PSC is used to notify the UEs that this is a WCDMA system. The PSC also provides them with a reference to synchronize themselves to the WCDMA slots. In other words after decoding the PSC the UE knows: • That it has found a WCDMA system. • When the slots start. So the UE knows when to look for the secondary synchronization codes. There are sixteen SSCs which are arranged into 64 unique combinations to identify the scrambling code group that the cell belongs to. In other words after decoding the SSC the UE knows two more things:

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5 WCDMA procedures EN/LZT 123 7279 R4A - 133 - • Which scrambling code group the primary scrambling code belongs to. • When the next WCDMA frame is going to start. " Broadcast by RBS First 256 chips of every P-CCPCH slot " Allows UE to achieve fast synchronization in an asynchronous system " Primary Synchronization Code PSC Fixed 256-chip sequence with base period of 16 chips Provides fast positive indication of a WCDMA system Allows fast asynchronous slot synchronization " Secondary Synchronization Codes SSC A set of 16 codes each 256 chips long Codes are arranged into one of 64 unique permutations Specific arrangement of SSC codes provide UE with frame timing Scrambling Code Group P-CCPCH PSC + SSC + BCH 2304 Chips 256 Chips 3GPP TS 25.213 ¶ 5.2.3 3GPP TS 25.213 ¶ 5.2.3 Broadcast Data 18 bits SSC i PSC Figure 5-3: Synchronization Codes i.e. PSC and SSC. Figure 5-4 shows how the PSC is transmitted to convey the slot timing to the UEs. As can be seen the code and the inverse of the code are sent in accordance with a particular pattern. The PSC is chosen to have a good periodic auto correlation property. The primary SCH is used to acquire the timing for the secondary SCH and it consists of an un-modulated code of length 256 chips which is transmitted once every slot. The primary synchronization code is the same for all cells in the system and is transmitted in line with the slot boundary.

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WCDMA Air Interface - 134 - EN/LZT 123 7279 R4A let a 1 1 1 1 1 1 -1 -1 1 -1 1 -1 1 -1 -1 1 PSC1...256 a a a -a -aa -a -a a a a -a a -a a a 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 Frame 15 slots 10 mSec Note: PSC is transmitted “Clear” Without scrambling 3GPP TS 25.213 ¶ 5.2.3 3GPP TS 25.213 ¶ 5.2.3 Broadcast Data 18 bits SSC i 2304 Chips 256 Chips SCH P-CCPCH PSC Figure 5-4: Primary Synchronization Code. Figure 5-5 shows how the PSC is used to provide the UE with the required slot synchronization. In practice this is used to tune a matched filter to the timing of each slot. The slot timing of the cell can be obtained by detecting peaks in the matched filter output. BCH Data PSC 1 BCH Data PSC 2 BCH Data PSC 3 BCH Data PSC 4 BCH Data PSC 15 Matched Filter Matched to PSC 10 mSec Frame 15 slots x 666.666 uSec Matched Filter Output time P-CCPCH PSC 3GPP TS 25.214 Annex C 3GPP TS 25.214 Annex C Figure 5-5: Slot Synchronization Using Primary Synchronization Code. The SSC is chosen from a set of sixteen different codes depending on which of the 64 different scrambling code groups the cell belongs to. Figure 5-6 shows how the sixteen SSCs are arranged into one of 64 unique patterns. The UEs can tell from the order in which the codes are transmitted which scrambling code group the cell belongs to. Another benefit of decoding these is that once the sixteen SSCs have been received the UE knows the cell frame timing.

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5 WCDMA procedures EN/LZT 123 7279 R4A - 135 - slot number Scrambling Code Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Group 1 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16 Group 2 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10 Group 3 1 2 1 15 5 5 12 16 6 11 2 16 11 15 12 • • • • • • • • • Group 62 9 10 13 10 11 15 15 9 16 12 14 13 16 14 11 Group 63 9 11 12 15 12 9 13 13 11 14 10 16 15 14 16 Group 64 9 12 10 15 13 14 9 14 15 11 11 13 12 16 10 Note: The SSC patterns positively identify one and only one of the 64 Scrambling Code Groups. This is possible because no cyclic shift of any SSC is equivalent to any cyclic shift of any other SSC. 3GPP TS 25.213 ¶ 5.2.3 3GPP TS 25.213 ¶ 5.2.3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 Frame 15 slots 10 mSec SSC 1 SSC 2 SSC 3 SSC 4 SSC 5 SSC 6 SSC 7 SSC 8 SSC 9 SSC 10 SSC 11 SSC 12 SSC 13 SSC 14 SSC 15 SSC 16 SSC i SSC 1 SSC 15 Figure 5-6: Secondary Synchronization Code Group. Sixteen fixed 256- bit codes. Codes arranged into one of 64 patterns Figure 5-7 shows how the UE achieves frame synchronization after receiving sixteen secondary synchronization codes. This is done by correlating the received signal with all possible secondary SCH code sequences and identifying the maximum correlation value. Because the cyclic shifts of the sequence are unique the code group and the frame synchronization are determined. BC H Da t a SSC 1 BC H Da t a SSC 2 BC H Da t a SSC 3 BC H Da t a SS C 4 BC H Da t a SS C 15 M a tc h e d Filte r M a tc h e d to S S C c o de g ro u p pa tte rn 1 10 m S e c F r am e 1 5 slo ts x 6 6 6.6 6 6 u S e c Ma t c h e d F ilte r Ou t p u t tim e SS C 1 SS C 2 SS C 8 SSC 1 SS C 10 SS C 15 SS C 8 SS C 9 SS C 16 SS C 2 SS C 7 SSC 10 SS C 7 SS C 16 SS C 15 S S C C o de G r oup P a tte r n pr ov id e s • F ra m e S y nc hro n iz a tio n • P o s itiv e ID of S c ra m b ling C o d e G ro u p R e m e m ber n o cy clic shift of a n y S S C is eq u a l to an y oth e r S S C Figure 5-7: Frame Synchronization using SSC. Figure 5-8 summarizes how all these steps are performed by the UE to achieve synchronization.

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WCDMA Air Interface - 136 - EN/LZT 123 7279 R4A Initiate Cell Synchronization P-CCPCH PSC + SSC + BCH UE Monitors Primary SCH code detects peak in matched filter output Slot Synchronization Determined ------ UE Monitors Secondary SCH code detects SCG and frame start time offset Frame Synchronization and Code Group Determined ------ UE Determines Scrambling Code by correlating all possible codes in group Scrambling Code Determined ------ UE Monitors and decodes BCH data BCH data Super-frame synchronization determined ------ Cell Synchronization Complete UE adjusts transmit timing to match timing of BS + 1.5 Chips Figure 5-8: UE Acquisition and Synchronization. When the UE has synchronized and found the scrambling code of the cell it can decode the system information BCH sent on the P- CCPCH. RANDOM ACCESS PROCEDURE Random access is a process where a UE requests access to the system and the network answers the request and allocates a dedicated channel to the UE. Random access happens whenever the UE needs to contact the network for example call setup location updating and PDP Context Activation. This process is also carried when the UE is sending PS data in Cell_FACH state. It is important to minimize the transmitted power during the random access because excessive power will degrade the WCDMA system capacity. This is essential since the random access transmission power cannot be controlled by the inner loop power control. Initial transmission with low power means a long time to access. On the other hand high power during the initial access causes high interference to other users. Figure 5-9 shows how the UE sends access preambles to the cell until it receives an acknowledgement in the AICH before sending the RACH message.

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5 WCDMA procedures EN/LZT 123 7279 R4A - 137 - Pre- amble Pre- amble Pre- amble AICH RACH No Ind. No Ind. Acq. Ind. RACH message part UE Identification UE BS 3GPP TS 25.211 ¶ 7.3 3GPP TS 25.211 ¶ 7.3 4096 chips 1.066 msec Figure 5-9: Random Access procedure. Prior to initiating a random access procedure the UE reads system information to receive: 1. The preamble scrambling code for this cell 2. The available random access signatures and set of available RACH sub-channels 3. The available spreading factors for the message part 4. The message length 10 ms or 20 ms 5. Initial preamble power parameter 6. The power-ramping factor Power Ramp Step integer 0 7. The parameter preamble Retrans Max integer 0 8. The AICH transmission timing parameter 0 or 1 9. The power offset ∆P pm between preamble and the message part. 10. Transport Format parameters Random Access Preamble Signature Figure 5-10 shows the sixteen available random access signatures.

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WCDMA Air Interface - 138 - EN/LZT 123 7279 R4A The UE will use one of these when sending the preamble. When the cell replies on the AICH it will use the same signature to distinguish which UE it is responding to. It must be remembered that several UEs could be sending preambles at the same time. These preamble signatures are orthogonal codes. Therefore the cell can identify each user making random access. Random Access Preamble Signature Symbols Signature P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 2 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 3 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 4 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 5 1 -1 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1 6 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 1 1 7 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1 1 -1 8 1 1 1 1 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 9 1 -1 1 -1 1 -1 1 -1 -1 1 -1 1 -1 1 -1 1 10 1 1 -1 -1 1 1 -1 -1 -1 -1 1 1 -1 -1 1 1 11 1 -1 -1 1 1 -1 -1 1 -1 1 1 -1 -1 1 1 -1 12 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 1 1 1 1 13 1 -1 1 -1 -1 1 -1 1 -1 1 -1 1 1 -1 1 -1 14 1 1 -1 -1 -1 -1 1 1 -1 -1 1 1 1 1 -1 -1 15 1 -1 -1 1 -1 1 1 -1 -1 1 1 -1 1 -1 -1 1 Figure 5-10: Random Access Preamble Signature Keywords about the preamble: • Preamble codes are 16-long Orthogonal Codes. • Preamble P 0 P 1 … P 15 repeated 256 times 4096 chips total. • Preamble codes help the cell distinguish between UEs making simultaneous Random Access attempts. Random Access Scrambling Codes Also included in the system information is the scrambling code that should be used by UEs accessing the cell. Figure 5-11 shows that cell 1 is transmitting a message like “All UEs accessing this cell shall use random access preamble scrambling code n1”. Cell 2 would be transmitting a message like “All UEs accessing this cell shall use random access preamble scrambling code n2”.

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5 WCDMA procedures EN/LZT 123 7279 R4A - 139 - “All UE accessing this cell shall use Random Access Preamble Spreading Code n2 ” “All UE accessing this cell shall use Random Access Preamble Spreading Code n1 ” 3GPP TS 25.213 ¶ 4.3.3 3GPP TS 25.213 ¶ 4.3.3 Figure 5-11: Random Access Scrambling Codes.

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WCDMA Air Interface - 140 - EN/LZT 123 7279 R4A Random Access Offset Timing Figure 5-12 shows the access slots of AICH and PRACH and their relative spacing. There are fifteen access slots per two frames and they are spaced 5120 chips apart. These are used to coordinate the timing of the RACHs. The figure also shows the twelve sub- channels of RACH. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Access slot set 1 Access slot set 2 AICH access slot RX at UE PRACH access slot TX at UE RACH sub-channel number P P P P P P P P P 0 1 11 2 3 • • 10 radio frame: 10 ms radio frame: 10 ms SFN mod 2 0 SFN mod 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 + every 12 th access slot + every 12 th access slot + every 12 th access slot + every 12 th access slot + every 12 th access slot + every 12 th access slot Figure 5-12: Random Access Procedure. Set of available RACH sub- channels determined by upper layers sent in system information. UE derives available access slots in the next full access slot set and selects slot based on pseudo-random algorithm.

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5 WCDMA procedures EN/LZT 123 7279 R4A - 141 - DEDICATED CHANNEL PROCEDURE In Figure 5-13 the establishment of a dedicated channel in the case of a mobile terminated call is shown. UE in Idle Mode 1. PI on the PICH 2. PCH message on the S-CCPCH 3. UE ramps up the power by sending preambles 4. RBS responds on the AICH 5. UE sends the RACH message 6. FACH message on S-CCPCH 7. DL-DPCH ramp up 8. UE sends UL-DPCH DPCH established Figure 5-13: Dedicated channel establishment-mobile terminated call 1. The UE is in idle mode and periodically listens to its PI on the PICH which is set to 1 when the UE is paged. 2. The actual paging message is initiated from the CN and is sent to the UE on the PCH that is mapped onto the S- CCPCH. 3. The UE reads system information to calculate the initial preamble power. The power is ramped up. 4. When the UE has achieved the correct power level on the preamble the RBS responds on the AICH. 5. The UE sends the RACH message: “RRC Connection Request” to the RNC to request for a dedicated channel. 6. The RNC checks available resources with admission control and sends a “RRC Connection Setup” message on FACH. This message gives information about the dedicated channel to be setup.

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WCDMA Air Interface - 142 - EN/LZT 123 7279 R4A 7. The transmission of the DL-DPCH is started and the power is ramped up. 8. The UE responds by sending the “RRC Connection Setup Complete” message on the UL-DPCH. Finally the DPCH is established and data can start to be transmitted and the inner loop power control loop is starting. WCDMA SOFT HANDOVER In the WCDMA RAN the RBSs are asynchronous and the timing is arbitrary. The UE has to inform the network about the timing difference in the case of soft handover see Figure 5-14. Data 2 TFCI Data 1 TPC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Pilot CPICH 2 CPICH 2 CPICH 2 CPICH 1 CPICH 1 CPICH 1 DPCCH/DPDCH DPCCH/DPDCH DPCCH/DPDCH CPICH 2 CPICH 1 DPCCH/DPDCH T offset 10 msec frame BS 1 BS 2 DPCCH/DPDCH DPCCH/DPDCH DPCCH/DPDCH DPCCH/DPDCH 10 msec DPCCH/DPDCH frame 0.666 msec DPCCH/DPDCH slot Figure 5-14: WCDMA base stations have asynchronous timing reference. IS95/cdma2000 RBSs are synchronized to GPS. Figure 5-15 shows the first four steps of WCDMA soft handover. 2 UE measures CPICH power and time delay from adjacent cells 3 UE Reports measurements to RNC 1 RNC informs UE of neighboring cell information 4 RNC decides the handover strategy CPICH 2 CPICH 2 CPICH 2 CPICH 1 CPICH 1 CPICH 1 DPCCH/DPDCH DPCCH/DPDCH DPCCH/DPDCH CPICH 2 CPICH 1 DPCCH/DPDCH T offset 10 msec frame RBS 1 RBS 2 RNC UE Reports T offset to RNC

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5 WCDMA procedures EN/LZT 123 7279 R4A - 143 - Figure 5-15: Soft handover 1 1. The RNC informs the UE of the neighboring cells to be measured on for soft handover 2. The UE measures CPICH quality and time offset T offset of the cells in the neighboring list. 3. When the soft handover criterias are fulfilled UE sends a measurement report to the RNC including the time offset. 4. The RNC will then decide if a handover should be performed based on these measurements. Step five to eight of the soft handover procedure are shown in Figure 5-16. 6 UE Rake Receiver Synchronizes to RBS2 DPCCH/DPDCH 7 UE in soft handover with RBS1 and RBS2 DPCCH/DPDCH’s 5 RNC Commands RBS2 to adjust DPCCH/DPDCH’s timing by T offset 8 When RBS2 sufficiently strong compared to RBS1 delete RBS1. CPICH 1 CPICH 1 CPICH 1 DPCCH/DPDCH DPCCH/DPDCH DPCCH/DPDCH CPICH 2 CPICH 2 CPICH 2 CPICH 2 CPICH 1 DPCCH/DPDCH T offset 10 msec frame RBS 1 RBS 2 RNC UE Reports T offset to RNC RNC Commands RBS2 to adjust DPCH timing by T offset DPCCH/DPDCH DPCCH/DPDCH DPCCH/DPDCH DPCCH/DPDCH T offset Figure 5-16: Soft Handover 2 5. The RNC commands RBS 2 to adjust the DPCH timing by T offset . 6. The rake receiver in the UE will then synchronize to the dedicated physical data and control channels DPDCH DPCCH of RBS 2. 7. The UE is now in soft handover and listens to both RBS 1 and RBS 2. 8. Finally the signal from RBS 2 is sufficiently strong to allow the connection from RBS 1 to be dropped. 9. THE END

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6 Acronyms and Abbreviations EN/LZT 123 7279 R4A - 145 - 6 Acronyms and Abbreviations

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6 Acronyms and Abbreviations EN/LZT 123 7279 R4A - 147 - AAL2 ATM Adaptation Layer type 2 ACK Acknowledgement AICH Acquisition Indicator Channel ALCAP Access Link Control Application Part AM Acknowledged Mode AMR Adaptive MultiRate speech codec AP Access Preamble ARQ Automatic Repeat Request AS Access Stratum ASC Access Service Class ATM Asynchronous Transfer Mode AUTN Authentication Token BCCH Broadcast Control Channel BCH Broadcast Control Channel BCFE Broadcast Control Functional Entity BER Bit Error Rate BLER Block Error Rate BMC Broadcast/Multicast Control BSS Base Station Sub-system BSSMAP Base Station System Management Application Part CC Call Control CCCH Common Control Channel CCPCH Common Control Physical Channel CCTrCH Coded Composite Transport Channel CFN Connection Frame Number CK Cipher Key CM Connection Management CN Core Network CPCH Common Packet Channel CPICH Common Pilot Channel CRC Cyclic Redundancy Check CRNC Controlling RNC C-RNTI Cell RNTI CS Circuit Switched CTCH Common Traffic Channel DCA Dynamic Channel Allocation DCCH Dedicated Control Channel DCFE Dedicated Control Functional Entity DCH Dedicated Channel DC-SAP Dedicated Control SAP DL Downlink DPCCH Dedicated Physical Control Channel DPCH Dedicated Physical Channel DRAC Dynamic Resource Allocation Control

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WCDMA Air Interface - 148 - EN/LZT 123 7279 R4A DRNC Drift RNC DRNS Drift RNS DRX Discontinuous Reception DSCH Downlink Shared Channel DTCH Dedicated Traffic Channel DTX Discontinuous Transmission EP Elementary Procedure FACH Forward Access Channel FAUSCH Fast Uplink Signalling Channel FDD Frequency Division Duplex FFS For Further Study FN Frame Number FP Frame Protocol ID Identifier GSM Global System for Mobile Communication IE Information element IMEI International Mobile Equipment Identity IMSI International Mobile Subscriber Identity IP Internet Protocol ISCP Interference on Signal Code Power KSI Key Set Identifier L1 Layer 1 L2 Layer 2 L3 Layer 3 LAI Location Area Identity MAC Medium Access Control MAC The Message Authentication Code included in AUTN computed using f1 MCC Mobile Country Code MM Mobility Management MNC Mobile Network Code MO Mobile Originating Call MS Mobile Station MSC Mobile services Switching Centre MT Mobile Terminal MTC Mobile Terminated Call NAS Non Access Stratum NBAP Node B Application Protocol Nt-SAP Notification SAP NW Network O Optional ODMA Opportunity Driven Multiple Access PCCH Paging Control Channel P-CCPCH Primary Common Control Physical Channel

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6 Acronyms and Abbreviations EN/LZT 123 7279 R4A - 149 - PCH Paging Channel PDCP Packet Data Convergence Protocol PDSCH Physical Downlink Shared Channel PDU Protocol Data Unit PHY Physical Layer PICH Paging Indicator Channel PLMN Public Land Mobile Network PNFE Paging and Notification Control Functional Entity PRACH Physical Random Access CHannel PS Packet Switched PSCH Physical Synchronisation Channel PSTN Public Switched Telephone Network P-TMSI Packet Temporary Mobile Subscriber Identity PUSCH Physical Uplink Shared Channel Q Quintet UMTS authentication vector QoS Quality of Service RA Routing Area RAB Radio Access Bearer RACH Random Access Channel RAI Routing Area Identity RAN Radio Access Network RANAP Radio Access Network Application Part RB Radio Bearer RFE Routing Functional Entity RL Radio Link RLC Radio Link Control RNC Radio Network Controller RNS Radio Network Subsystem RNSAP Radio Network Subsystem Application Part RNTI Radio Network Temporary Identifier RRC Radio Resource Control RSCP Received Signal Code Power RSSI Received Signal Strength Indicator RT Real Time SAI Service Area Identifier SAP Service Access Point SCCP Signalling Connection Control Part S-CCPCH Secondary Common Control Physical Channel SCFE Shared Control Function Entity SCH Synchronization Channel SDU Service Data Unit SF Spreading Factor SFN System Frame Number

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WCDMA Air Interface - 150 - EN/LZT 123 7279 R4A SGSN Serving GPRS Support Node SHCCH Shared Control Channel SIR Signal to Interference Ratio SMS Short Message Service SRNC Serving RNC SRNS Serving RNS S-RNTI SRNC – RNTI SSDT Site Selection Diversity Transmission TDD Time Division Duplex TE Terminal Equipment TEID Tunnel Endpoint Identifier TF Transport Format TFC Transport Format Combination TFCI Transport Format Combination Indicator TFCS Transport Format Combination Set TFS Transport Format Set TME Transfer Mode Entity TM Transparent Mode TMD Transparent Mode Data TMSI Temporary Mobile Subscriber Identity TPC Transmit Power Control Tr Transparent TrCH Transport Channel TTI Transmission Time Interval Tx Transmission UARFCN UMTS Absolute Radio Frequency Channel Number UE User Equipment UEA UMTS Encryption Algorithm UIA UMTS Integrity Algorithm UL Uplink UM Unacknowledged Mode UMD Unacknowledged Mode Data UMTS Universal Mobile Telecommunication System UNACK Unacknowledgement URA UTRAN Registration Area U-RNTI UTRAN-RNTI USCH Uplink Shared Channel UTRA UMTS Terrestrial Radio Access UTRAN UMTS Terrestrial Radio Access Network VLR Visitor Location Register XRES Expected Response

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